Stability of the human sperm DNA methylome to folic acid fortification and short-term supplementation

STUDY QUESTION

Do short-term and long-term exposures to low-dose folic acid supplementation alter DNA methylation in sperm?

SUMMARY ANSWER

No alterations in sperm DNA methylation patterns were found following the administration of low-dose folic acid supplements of 400 μg/day for 90 days (short-term exposure) or when pre-fortification of food with folic acid and post-fortification sperm samples (long-term exposure) were compared.

WHAT IS KNOWN ALREADY

Excess dietary folate may be detrimental to health and DNA methylation profiles due to folate's role in one-carbon metabolism and the formation of S-adenosyl methionine, the universal methyl donor. DNA methylation patterns are established in developing male germ cells and have been suggested to be affected by high-dose (5 mg/day) folic acid supplementation.

STUDY DESIGN, SIZE, DURATION

This is a control versus treatment study where genome-wide sperm DNA methylation patterns were examined prior to fortification of food (1996-1997) in men with no history of infertility at baseline and following 90-day exposure to placebo (n = 9) or supplement containing 400 μg folic acid/day (n = 10). Additionally, pre-fortification sperm DNA methylation profiles (n = 19) were compared with those of a group of post-fortification (post-2004) men (n = 8) who had been exposed for several years to dietary folic acid fortification.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Blood and seminal plasma folate levels were measured in participants before and following the 90-day treatment with placebo or supplement. Sperm DNA methylation was assessed using the whole-genome and genome-wide techniques, MassArray epityper, restriction landmark genomic scanning, methyl-CpG immunoprecipitation and Illumina HumanMethylation450 Bead Array.

MAIN RESULTS AND THE ROLE OF CHANCE

Following treatment, supplemented individuals had significantly higher levels of blood and seminal plasma folates compared to placebo. Initial first-generation genome-wide analyses of sperm DNA methylation showed little evidence of changes when comparing pre- and post-treatment samples. With Illumina HumanMethylation450 BeadChip arrays, no significant changes were observed in individual probes following low-level supplementation; when compared with those of the post-fortification cohort, there were also few differences in methylation despite exposure to years of fortified foods.

LARGE SCALE DATA

Illumina HumanMethylation450 BeadChip data from this study have been submitted to the NCBI Gene Expression Omnibus under the accession number GSE89781.

LIMITATIONS, REASONS FOR CAUTION

This study was limited to the number of participants available in each cohort, in particular those who were not exposed to early (pre-1998) fortification of food with folic acid. While genome-wide DNA methylation was assessed with several techniques that targeted genic and CpG-rich regions, intergenic regions were less well interrogated.

WIDER IMPLICATIONS OF THE FINDINGS

Overall, our findings provide evidence that short-term exposure to low-dose folic acid supplements of 400 μg/day, over a period of 3 months, a duration of time that might occur during infertility treatments, has no major impact on the sperm DNA methylome.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by a grant to J.M.T. from the Canadian Institutes of Health Research (CIHR: MOP-89944). The authors have no conflicts of interest to declare.

Low seminal plasma folate concentrations are associated with low sperm density and count in male smokers and nonsmokers

OBJECTIVE

To measure folate levels in seminal plasma from smokers and nonsmokers and to evaluate relationships between seminal plasma folate levels and both folate nutriture and semen quality measures.

DESIGN

Observational study.

SETTING

United States Department of Agriculture, Western Human Nutrition Research Center, Presidio of San Francisco, San Francisco, California.

PATIENT(S)

Healthy male smokers (n=24) and nonsmokers (n=24).

MAIN OUTCOME MEASURE(S)

Blood levels of plasma folate and homocysteine, seminal plasma total, non-methyl- and 5-methyltetrahydrofolate concentrations, and total sperm count and density.

RESULTS

Total seminal plasma folate concentrations were on average 1.5 times higher than blood plasma folate concentrations in all men. Seminal plasma folates contained 5-methyltetrahyrdofolate (74% of total) and non-methyltetrahydrofolates (26% of total); all samples had less than four glutamyl residues. Total and 5-methyltetrahydrofolate concentrations correlated significantly with blood plasma folate and homocysteine concentrations. Seminal plasma non-methyltetrahydrofolate levels correlated significantly with sperm density and total sperm count. Seminal plasma of smokers contained a proportionally lower concentration of non-methyltetrahydrofolates compared with nonsmokers.

CONCLUSION(S)

Seminal plasma total folate and 5-methyltetrahydrofolate concentrations reflect folate nutriture. The non-methyltetrahydrofolate fraction of seminal plasma may be important for male reproductive function.

Urinary excretion of folate catabolites responds to changes in folate intake more slowly than plasma folate and homocysteine concentrations and lymphocyte DNA methylation in postmenopausal women

Folate turnover involves urinary excretion, fecal excretion, and catabolism that involves cleavage of the C9-N10 bond to yield pterins and para-aminobenzoylglutamate (pABG). Little is known about the relationship between the function of folate pools and their rates of catabolism. We report here an investigation of excretion of urinary pABG and its primary excretory form, para-acetamidobenzoylglutamate (ApABG) in samples collected during a previously published study of postmenopausal women. Ten women (49-63 y) were fed a low folate diet (56 microg/d) supplemented with folic acid to yield total folate intakes of 195 microg/d (d 1-5), 56 microg/d (d 6-41), 111 microg/d (d 42-69), 286 microg/d (d 70-80) and 516 microg/d (d 81-91). This caused changes in plasma folate, plasma homocysteine and global methylation of lymphocyte DNA. For each subject, a 7-d pooled urine sample was collected over d 1-7, 36-42, 64-70 and 85-91. ApABG constituted >85% of total catabolite excretion, and folate intake did not significantly influence ApABG or pABG excretion. The molar ratio of total catabolite excretion/folate intake varied significantly, with ratios of 1.0 +/- 0.17 (d 1-7), 3.0 +/- 0.55 (d 36-42), 1.1 +/- 0.18 (d 64-70) and 0. 33 +/- 0.054 (d 85-91). These observations indicate that the rate of folate catabolite excretion is related mainly to masses of slow-turnover folate pools governed by long-term folate intake. Folate pools functioning in some forms of methyl group metabolism respond to dietary changes in folate intake much more rapidly.

Passive smoking induces oxidant damage preventable by vitamin C

The deleterious effects of cigarette smoking on antioxidant protection and chronic disease risk are well known. Recent studies show that exposure of nonsmokers to environmental tobacco smoke results in increased oxidant damage linked to heart and respiratory diseases. The new findings provide support for efforts to minimize exposure of nonsmokers to environmental tobacco smoke and oxidizing air pollutants and demonstrate the importance of vitamin C for antioxidant protection.

Ascorbate is depleted by smoking and repleted by moderate supplementation: a study in male smokers and nonsmokers with matched dietary antioxidant intakes

BACKGROUND

Lack of reliable dietary data has hampered the ability to effectively distinguish between effects of smoking and diet on plasma antioxidant status. As confirmed by analyses of comprehensive food-frequency questionnaires, the total dietary intakes of fruit and vegetables and of dietary antioxidants were not significantly different between the study groups in the present study, thereby enabling isolation of the effect of smoking.

OBJECTIVE

Our objective was to investigate the effect of smoking on plasma antioxidant status by measuring ascorbic acid, alpha-tocopherol, gamma-tocopherol, beta-carotene, and lycopene, and subsequently, to test the effect of a 3-mo dietary supplementation with a moderate-dose vitamin cocktail.

DESIGN

In a double-blind, placebo-controlled design, the effect of a vitamin cocktail containing 272 mg vitamin C, 31 mg all-rac-alpha-tocopheryl acetate, and 400 microg folic acid on plasma antioxidants was determined in a population of smokers (n = 37) and nonsmokers (n = 38). The population was selected for a low intake of fruit and vegetables and recruited from the San Francisco Bay area.

RESULTS

Only ascorbic acid was significantly depleted by smoking per se (P < 0.01). After the 3-mo supplementation period, ascorbic acid was efficiently repleted in smokers (P < 0.001). Plasma alpha-tocopherol and the ratio of alpha- to gamma-tocopherol increased significantly in both supplemented groups (P < 0.05).

CONCLUSIONS

Our data suggest that previous reports of lower concentrations of plasma vitamin E and carotenoids in smokers than in nonsmokers may primarily have been caused by differences in dietary habits between study groups. Plasma ascorbic acid was depleted by smoking and repleted by moderate supplementation.

Evidence that diet modification reduces in vivo oxidant damage

Because few trials have studied the antioxidant effects of diets rather than vitamin supplements, the results of a recent trial that altered fruit, vegetable, and fat intake in healthy adults are especially valuable. The findings support the hypothesis that changing dietary patterns may decrease the risk of atherosclerosis by favorably altering the balance of oxidant defense and damage.

Folate nutriture alters choline status of women and men fed low choline diets

Choline and folate share methylation pathways and, in studies of rats, were shown to be metabolically inter-related. To determine whether choline status is related to folate intake in humans, we measured the effect of controlled folate depletion and repletion on the plasma choline and phosphatidylcholine concentrations of 11 healthy men (33-46 y) and 10 healthy women (49-63 y) fed low-choline diets in two separate metabolic unit studies. Total folate intake was varied by supplementing low folate (25 and 56 microg/d for men and women, respectively) and low choline (238 and 147 mg/d for men and women, respectively) diets with pteroylglutamic acid for 2-6 wk following folate-depletion periods of 4-5 wk. The low folate/choline intakes resulted in subclinical folate deficiencies; mean plasma choline decreases of 28 and 25% in the men and women, respectively; and a plasma phosphatidylcholine decrease of 26% in the men (P < 0. 05). No functional choline deficiency occurred, as measured by serum transaminase and lipid concentrations. The decreases in choline status measures returned to baseline or higher upon moderate folate repletion and were more responsive to folate repletion than plasma folate and homocysteine. Feeding methionine supplements to the men did not prevent plasma choline depletion, indicating that folate is a more limiting nutrient for these methylation pathways. The results indicate that 1) choline is utilized as a methyl donor when folate intake is low, 2) the de novo synthesis of phosphatidylcholine is insufficient to maintain choline status when intakes of folate and choline are low, and 3) dietary choline is required by adults in an amount > 250 mg/d to maintain plasma choline and phosphatidylcholine when folate intake is low.

Vitamin C nutriture and risk of atherosclerotic heart disease

There is substantial evidence for a role of dietary antioxidants in the prevention of cardiovascular disease, but evidence for a protective effect of vitamin C is inconclusive. Two recent reports add to the supporting evidence and provide some new observations. The first study, a 5-year prospective population study of Finnish men, suggests that vitamin C-deficient men may be at increased risk of myocardial infarction. The second study suggests that vitamin C may play a role in preventing manifestations of existing coronary artery disease, rather than in limiting disease progression. Although these results suffer from the limitations of observational studies, they provide impetus for further investigation.

Micronuclei in lymphocytes and exfoliated buccal cells of postmenopausal women with dietary changes in folate

Folate deficiency is associated with anemia, birth defects, cancer and neuropsychiatric disorders. The purpose of this study was to determine if a moderate folate deficiency during controlled changes in folate intake would affect chromosomal damage in lymphocytes and buccal cells. A study of nine healthy postmenopausal women volunteers (age 49-63 years) was carried out in a metabolic unit (baseline week with folate intake of 195 microg/day, five-week depletion at 56 microg/day, and gradual repletion including four weeks at 111 microg/day, 11 days at 286 microg/day and 9 days at 516 microg/day). Plasma folate, vitamin B-12, and homocysteine were measured weekly. Cytogenetic damage was assessed by scoring micronucleus (MN) frequency in lymphocytes and buccal cells three times: (1) at the beginning of the study, (2) at the end of depletion, and (3) after repletion. The MN frequency increased in binucleated lymphocytes, as well as in all lymphocytes, after depletion (p=0.037), and later decreased following repletion (p=0. 028). Both kinetochore-positive and kinetochore-negative MN were increased after depletion (p=0.015 and 0.028), but after repletion only the change in kinetochore-positive MN was statistically significant (p=0.048). The main variables affecting MN were: (1) vitamin B-12 level, (2) plasma folate level, and (3) baseline frequency of MN. The MN frequency in exfoliated buccal cells was decreased after dietary supplementation of 516 microg/day folate (p=0.010). Thus, low folate, without clinical symptoms of anemia, results in higher levels of cytogenetic damage in both the blood and oral cavity of postmenopausal women.

Individual variability in homocysteine response to folate depletion: an unusual case

Research within the past decade has shown that even moderately elevated plasma homocysteine concentrations are associated with increased risk of vascular disease. A variety of genetic and nutritional factors can affect homocysteine concentrations, with folate nutriture being one of the most influential. Plasma homocysteine responses of healthy adults to folate depletion and repletion vary substantially, even when many nutritional and lifestyle factors are normalized in a metabolic unit. The case of a woman with a highly exaggerated homocysteine response to moderate folate depletion is presented. A variety of possible factors relating to homocystine metabolism are discussed, yet no convincing explanation for the unusual pattern is apparent. The case demonstrates that the homocysteine response to folate can be highly variable between individuals, and suggests that further research on the genetic determinants of the human folate requirement is warranted.

Moderate folate depletion increases plasma homocysteine and decreases lymphocyte DNA methylation in postmenopausal women

To determine the human folate requirement on the basis of changes in biochemical pathways, we studied the effect of controlled folate intakes on plasma homocysteine and lymphocyte DNA methylation and deoxynucleotide content in healthy postmenopausal women. Eight women (49-63 y of age) were housed in a metabolic unit and fed a low folate diet containing 56 microg/d of folate for 91 d. Folate intake was varied by supplementing 55-460 microg/d of folic acid (pteroylglutamic acid) to the diet to provide total folate intake periods of 5 wk at 56 microg/d, 4 wk at 111 microg/d and 3 wk at 286-516 microg/d. A subclinical folate deficiency with decreased plasma folate was created during the first two periods. This resulted in significantly elevated plasma homocysteine and urinary malondialdehyde, and lymphocyte DNA hypomethylation. The folate depletion also resulted in an increased ratio of dUTP/dTTP in mitogen-stimulated lymphocyte DNA and decreased lymphocyte NAD, changes suggesting misincorporation of uracil into DNA and increased DNA repair activity. The DNA hypomethylation was reversed with 286-516 microg/d of folate repletion, whereas the elevated homocysteine decreased with 516 but not 286 microg/d of folate. The results indicate that marginal folate deficiency may alter DNA composition and that the current RDA of 180 microg/d may not be sufficient to maintain low plasma homocysteine concentrations of some postmenopausal women.

'Spontaneous' genetic damage in man: evaluation of interindividual variability, relationship among markers of damage, and influence of nutritional status

The 'spontaneous' frequency of genetic damage (normal background) and the possible relationship of this damage to nutritional variables in humans were investigated in 22 subjects using several indices of genetic damage. The subjects were chosen, out of 122 initially analyzed, for being at the extremes of the highest and lowest values of one index of genetic damage, the frequency of micronucleated erythrocytes in peripheral blood. This index reflects chromosomal damage and loss in bone marrow erythropoietic cells. The assay for micronuclei is convenient but is restricted to splenectomized individuals because the human spleen removes micronucleated cells. The initial 122 subjects were splenectomized, but all were normal and healthy at the time of this study and none had a previous history of neoplastic disease. Factors investigated were stability of micronucleus frequency as a function of time, correlations among multiple markers of genetic damage, and influence on damage indices of nutritional variables, including blood levels of folate, B12 and antioxidant vitamins. Among different individuals, the range of values was 10-fold or more in the erythrocyte micronucleus, glycophorin A, plasma ascorbate and urinary 8-hydroxydeoxyguanosine (oxo8dG) assays, was approximately 6-fold in the lymphocyte micronucleus assay, and was 2-fold in the lymphocyte sister chromatid exchange (SCE) assay. Red blood cell folate and plasma folate, B12 and alpha-tocopherol values varied by up to 10-fold among individuals. Micronucleus frequencies in erythrocytes and peripheral blood lymphocytes ranged from < 0.3 to 16.9/1000 in mature red blood cells, < 1 to 33/1000 in reticulocytes, and 2.5 to 15/1000 in binucleate lymphocytes. Frequencies of glycophorin A variant erythrocytes ranged from 5.6 to 77.3 x 10(6) N/0 cells and 3.2 to 16.2 x 10(6) N/N cells, and oxo8dG excretion varied from 32 to 397 pmol/kg/day. Although a wide range of values was observed in each genetic endpoint, the extreme values for various endpoints of genetic damage were not observed in the same individuals. The frequency of micronucleated erythrocytes varied over time within individuals and indicated that individuals with the highest levels of damage exhibit greater variability than those with lower levels. In some subjects, frequencies of micronucleated erythrocytes changed dramatically over an interval of 2-3 years: four subjects with initial micronucleated reticulocyte frequencies of 20.4, 5.9, 6.4 and 33/1000 changed to 2.5, 20.5, 18.5 and 12/1000, respectively. Among more than 150 individuals we have studied, including the 64 individuals studied by Everson et al. [(1988) J. Natl. Cancer Inst., 80, 525-529] and Smith et al. [(1990) Cancer Res., 50, 5049-5054], the seven individuals with the highest observed frequencies of micronucleated erythrocytes all had exceptionally low values of plasma folate, red cell folate, or plasma B12, suggesting that folate and B12 status are the major determinants of the types of damage that lead to spontaneous micronucleus formation in erythrocytic cells.

Vitamin C nutriture has little short-term effect on vitamin E concentrations in healthy women

To determine whether the postulated sparing effect of vitamin E by ascorbic acid (AA) is important for human nutrition, we studied vitamin E status in 20 healthy pre-menopausal women (age 20-43 y) with high or low vitamin C intakes for 6 wk in a live-in metabolic unit. The experimental diet contained no fruits and vegetables and provided 5 mg/d of AA (Recommended Dietary Allowance = 60 mg/d), 3 mg/d of alpha-tocopherol (RDA = 10 mg/d) and 42 g/d of tocopherol-stripped safflower oil to increase the vitamin E requirement. Half of the subjects revived a daily AA supplement of 495 mg (high AA group). A biochemical ascorbate deficiency was attained in the low AA group as indicated by plasma AA concentrations that reached the lower limit of normal by study d 15. Oral doses (20 mg) of hexadeuterated RRR-alpha-tocopherol acetate (d6-alphaT) were given daily to all subjects on d 15-21. Measures of vitamin E status included d6-alphaT and unlabeled alpha-tocopherol concentrations in plasma, platelets, buccal cells and adipose. The levels of unlabeled alpha-tocopherol decreased over time in plasma and platelets and were unchanged for buccal cells and adipose, but were not significantly affected by AA intake. Likewise, the rise and fall of plasma and platelet d6-alpha T, and measures of lipid peroxidation, were not affected by AA intake. Although vitamin C nutriture did not significantly affect vitamin E status within the 6-wk time period of this experiment, further study of this question is warranted, because some of the present results indicate a trend toward sparing of tissue tocopherol by high AA intake.

Update on the biological characteristics of the antioxidant micronutrients: vitamin C, vitamin E, and the carotenoids

Under normal circumstances, free radicals that are produced through biological processes and in response to exogenous stimuli are controlled by various enzymes and antioxidants in the body. Laboratory evidence suggests that oxidative stress, which occurs when free radical formation exceeds the ability to protect against them, may form the biological basis of several acute medical problems, such as tissue injury after trauma, and chronic conditions, such as atherosclerosis and cancer. A potential role for the antioxidant micronutrients (vitamin C, vitamin E, and the carotenoids) in modifying the risk for conditions that may result from oxidative stress has stimulated intense research efforts, increased interest in micronutrient supplements, and heightened consumer interest in these compounds. Much remains to be learned, however, about the bioavailability, tissue uptake, metabolism, and biological activities of these micronutrients. These biological characteristics will ultimately determine their clinical usefulness in modulating oxidative stress. Also, whether the antioxidant mechanism explains their relationship with risk for acute and chronic disease in epidemiologic studies remains to be determined. Increased knowledge in this area of nutrition science will have an impact on both clinical dietetics practice and public health nutrition guidelines.

Oxidative damage and defense

Increased production of reactive oxygen species is a feature of most, if not all, human disease, including cardiovascular disease and cancer. Dietary antioxidants may be especially important in protecting against human diseases associated with free radical damage to cellular DNA, lipids, and proteins. Ascorbic acid is an effective water-soluble antioxidant, and epidemiologic studies suggest that increased ascorbate nutriture is associated with reduced risk of some degenerative diseases, especially cancer and eye cataracts. Population studies have also shown that high vitamin E intakes are associated with decreased risk of coronary heart disease, possibly as a result of inhibition of atherogenic forms of oxidized low-density lipoprotein. Recent data suggest that beta-carotene provides protection against lipid peroxidation in humans, as well as provitamin A activity. Yet, present data are not sufficient to quantitate micronutrient requirements needed to protect against oxidative damage. The antioxidant roles of many food constituents, such as polyphenols, have not been clarified. Most antioxidants can act as prooxidants under certain conditions, and more research is needed to determine the occurrence and importance of this in vivo. The few controlled intervention trials carried out so far have shown mixed results as to the potential of antioxidant supplements for reducing the incidence of chronic diseases. Definitive recommendations on antioxidant intakes for disease prevention must await evidence from controlled studies and intervention trials, some currently in progress. Overall, the present data suggest that protection against oxidative damage and related disease is best served by the variety of antioxidant substances found in fruit and vegetables.

In vivo methylation capacity is not impaired in healthy men during short-term dietary folate and methyl group restriction

Ten healthy adult men were fed a diet low in folate and exogenous methyl groups to study the effects on in vivo methylation capability. The men were housed in a metabolic unit for the entire 108 d of the study. After a 9-d baseline period (Period 1), the men were fed a soy-product-amino acid defined diet for 45 d, which provided 25 micrograms/d of folate for 30 d (Period 2) and, with a folate supplement, 99 micrograms/d for 15 d (Period 3). During Period 2 and Period 3, the low methionine and choline diet was supplemented with methionine for half the subjects to vary the dietary methyl group intake. The periods were then repeated over the next 54 d (Periods 4-6), with a crossover of methionine intakes in Period 5 and Period 6. A 1-g oral dose of nicotinamide was given at the end of each period and methylated urine metabolites determined. Other measures related to in vivo methylation capability included urine creatinine, and plasma and urine carnitine. Even with moderate folate depletion, none of these measures was decreased by low methionine and choline intakes. Plasma methionine concentrations were unchanged throughout. Limiting exogenous methyl group intake by restricting dietary methionine and choline did not impair in vivo methylation capabilities for the variables tested, even at low folate intake.

Homocysteine increases as folate decreases in plasma of healthy men during short-term dietary folate and methyl group restriction

Ten healthy adult men were fed a diet low in folate and exogenous methyl groups to study the effects on folate requirement and status. The men were housed in a metabolic unit for the entire 108-d study. After a 9-d base-line period (P1), the men were fed an amino acid-defined soybean product diet for 45 d, which provided 25 micrograms/d of folate for 30 d (P2) and (with a folate supplement) 99 micrograms/d for 15 d (P3). During P2 and P3, the low methionine and choline diet was supplemented with methionine for half the subjects to vary the dietary methyl group intake. The periods were then repeated over the next 54 d (P4-P6), with a cross-over of methionine intakes in P5 and P6. Restricting dietary methyl group intake did not increase the dietary folate requirement. Plasma total homocysteine rose during folate depletion and correlated inversely with plasma folate; however, the response of homocysteine to changes in folate intake varied among individuals from very strong to absent. The results support previous suggestions that increased plasma homocysteine concentrations provide a marker of functional folate deficiency, and further indicate that individuals may differ greatly in their susceptibility to hyperhomocysteinemia due to low folate intakes. Judged by the lack of normalization of high homocysteine concentrations during folate repletion, the current folate RDA for adult men may not provide the expected margin of protection.

Biochemical assessment of vitamins and trace metals

The choice of nutritional assessment tests must be made with care, as the available tests may reflect recent dietary intakes or body tissue stores to different degrees. The interpretation of nutritional assessment tests is complicated by the dynamic nature and broad range of nutrient intake and metabolism and by a relative lack of age- and sex-specific reference ranges. The latter problem can be minimized by the use of function-based methods, such as the measurement of vitamin-dependent red cell enzyme activities to assess B vitamin status; however, few suitable function-based methods are now available, and more research in this area is needed. Because calibration standards and quality control materials may not be readily available, laboratory analysts planning nutritional assessment testing must be especially careful in establishing the credibility of assays and the quality control program. Recent advances in analytic methodology include the specificity offered by HPLC techniques and methodologies that provide simultaneous determination of more than one nutrient (or form of nutrient) in a single procedure. Examples of the latter include HPLC methods that provide B vitamin or fat-soluble vitamin profiles, and emission spectrometry techniques that provide trace metal profiles. Further work in providing useful nutritional assessment profiles and convenient automated methods is needed.

Cellular ascorbate depletion in healthy men

To clarify the relationship of plasma ascorbic acid to cellular ascorbic acid levels, we determined plasma, lymphocyte, buccal cell and semen ascorbic acid in eight healthy men consuming controlled ascorbic acid intakes of 5, 10, 20, 60 or 250 mg/d over 13 wk while living in a metabolic unit. Levels of ascorbic acid in all four specimen types were significantly lower during the three lowest intakes (5, 10, or 20 mg/d) compared with the 60 or 250 mg/d intakes, but only plasma and lymphocyte ascorbic acid levels discriminated between these intakes unequivocally and with no overlap. Priority for maintenance of intracellular lymphocyte ascorbic acid was indicated by rapid repletion of lymphocytes compared with plasma and semen at 60 mg/d intake. Strong correlations of plasma with lymphocyte ascorbic acid within individuals indicated that plasma levels would reliably reflect low lymphocyte levels in nutrition monitoring surveys. Buccal cell ascorbic acid may be useful as a noninvasive screening test for ascorbic acid deficiency. Semen and sperm qualities were unchanged despite an average decline in semen ascorbic acid to 24% of baseline. Short-term ascorbic acid depletion in healthy men did not adversely affect sperm qualities related to fertility nor did moderate supplementation improve them.

Plasma carotenoid levels in human subjects fed a low carotenoid diet

The purpose of this study was to investigate the effect of a low carotenoid diet on plasma carotenoid levels in humans. Twelve healthy male subjects were fed a low carotenoid diet under controlled conditions for 13 wk in a live-in metabolic unit, as part of a study of vitamin C requirement. Plasma carotenoids (zeaxanthin/lutein, cryptoxanthin, lycopene, alpha-carotene, beta-carotene) were measured with HPLC on study days 2-3, 14-15, 35-36 and 63-64. The rate of decline was rapid between d 2-3 and d 14-15, when the concentration of each carotenoid decreased significantly (P less than 0.05). Although accurate figures for half-life are not possible without more frequent sampling points, mean plasma depletion half-life seemed to be less than 12 d for beta-carotene, alpha-carotene and cryptoxanthin, between 12 and 33 d for lycopene and between 33 and 61 d for zeaxanthin/lutein. Because the decline was not linear over the study period, these data suggest the possibility of at least two body pools of these compounds, with one pool having a more rapid turnover rate. Because there is a significant decline in plasma carotenoid levels within the first 2 wk of a low carotenoid diet, determination of levels of these compounds may be useful only in the assessment of short-term intake.

Ascorbic acid protects against endogenous oxidative DNA damage in human sperm

Damage to the DNA of germ cells can lead to mutation, which may result in birth defects, genetic diseases, and cancer. The very high endogenous rate of oxidative DNA damage and the importance of dietary ascorbic acid (AA) in preventing this damage has prompted an examination of these factors in human sperm DNA. The oxidized nucleoside 8-hydroxy-2'-deoxyguanosine (8-oxo-7,8-dihydro-2'-deoxyguanosine; oxo8dG), 1 of approximately 20 major products of oxidative damage to DNA, was measured in DNA isolated from human sperm provided by healthy subjects and compared to the seminal fluid AA levels. This relationship was studied in two groups. In a group of 24 free-living individuals 20-50 years old high levels of oxo8dG were correlated with low seminal plasma AA. The endogenous level of oxo8dG in this group was 13 fmol per microgram of DNA or approximately 25,000 adducts per sperm cell. The second group of individuals was maintained on a controlled diet that varied only in AA content. When dietary AA was decreased from 250 to 5 mg/day, the seminal fluid AA decreased by half and the level of oxo8dG in sperm DNA increased 91%. Repletion of dietary AA for 28 days (from 5 mg/day to 250 or 60 mg/day) caused a doubling in seminal fluid AA and reduced oxo8dG by 36%. These results indicate that dietary AA protects human sperm from endogenous oxidative DNA damage that could affect sperm quality and increase risk of genetic defects, particularly in populations with low AA such as smokers.

Immunocompetence and oxidant defense during ascorbate depletion of healthy men

To determine nonscorbutic effects of moderate vitamin C deficiency we measured immune function and oxidative damage in eight healthy men (25-43 y) who consumed 5-250 mg/d of ascorbic acid over 92 d on a metabolic unit. During ascorbic acid intakes of 5, 10, or 20 mg/d, subjects attained a state of moderate ascorbic acid deficiency as ascorbic acid concentrations in plasma, leucocytes, semen, and buccal cells dropped to less than 50% of baseline with no scorbutic symptoms observed. No changes in cell proliferation, erythrocyte antioxidant enzymes, and DNA strand breaks were observed; however, blood levels of glutathione and NAD(P) decreased during ascorbic acid deficiency, as did delayed hypersensitivity responsiveness. Concentrations of the oxidatively modified DNA base, 8-hydroxydeoxyguanosine in sperm DNA and fecapentaenes, ubiquitous fecal mutagens, were increased during ascorbic acid depletion. Moderate vitamin C deficiency, in the absence of scurvy, results in alteration of antioxidant chemistries and may permit increased oxidative damage.

Effects of ascorbic acid depletion and supplementation on periodontal health and subgingival microflora in humans

This study describes the relationship between varying ascorbate intake, periodontal status, and subgingival microflora as part of a multidisciplinary investigation of ascorbic acid (AA) metabolism in young men housed for 13 weeks in a nutrition suite that provided controlled periods of ascorbic acid depletion and repletion. Twelve medically healthy non-smoking men, aged 25 to 43 years, ate a rotating four-day diet adequate in all nutrients except ascorbic acid. Following an initial baseline period during which the subjects received 250 mg AA/day, the subjects received 5 mg AA/day for a 32-day depletion period. Eight of the 12 subjects participated in a subsequent 56-day repletion period designed to replace the reduced body AA pool slowly. Plasma and leukocyte ascorbate levels, Plaque Index, Gingival Index, probing depths, and attachment level were monitored at the beginning and end of the depletion and repletion periods. Subgingival plaque samples were obtained and examined for selected organisms by indirect immunofluorescence microscopy. A uniform oral hygiene program was reinforced after each examination. Ascorbate concentrations in plasma and leukocytes responded rapidly to changes in vitamin C intake. There were no significant changes in plaque accumulation, probing pocket depth, or attachment level during the study. In contrast, gingival bleeding increased significantly after the period of AA depletion and returned to baseline values after the period of AA repletion. However, no relationship could be demonstrated between either the presence or proportion of target periodontal micro-organisms and measures of bleeding or ascorbate levels.

Glutathione blood levels and other oxidant defense indices in men fed diets low in vitamin C

Because ascorbic acid is an important contributor to the oxidant defense system in body tissues, we studied the effects of a low dietary intake of ascorbic acid on various indicators of oxidant defense and oxidant damage. During a 13-wk study eight healthy men (25-43 y), residing in a live-in metabolic unit, were fed controlled diets containing different amounts of ascorbic acid for four consecutive periods: period 1 = 250 mg/d for 4 d; period 2 = 5 mg/d for 32 d; period 3 = 10 or 20 mg/d for 28 d and period 4 = 60 or 250 mg/d for 28 d. Measurements were made at several time intervals of the activities of glutathione peroxidase and superoxide dismutase in RBC, DNA strand breaks in mononuclear leucocytes, glutathione concentrations in plasma and RBC and NAD and NADP in RBC. After 60 d of low ascorbic acid intakes and associated with plasma ascorbic acid levels less than 6 mumol/L, the total glutathione concentration and the reduced glutathione:oxidized glutathione ratio were decreased in plasma. At the same time NAD and NADP levels in RBC were elevated. It seems that chronic marginal vitamin C deficiency states may be associated with selected biochemical changes in oxidant defense indices.

Assessment of human vitamin C status

Since no reliable functional markers of human vitamin C status have been demonstrated, determination of vitamin C levels in blood plasma and/or leukocytes remains the current choice for individual and population assessments. Newer analytical techniques, especially high-performance liquid chromatography, allow determination of reduced (ascorbic acid), oxidized (dehydroascorbic acid), or total amounts of vitamin C in biological specimens or foods. Plasma levels of vitamin C forms are easily determined but may not reflect tissue content as well as leukocyte levels. The vitamin C content of leukocyte cell types varies severalfold and, unlike plasma, leukocytes may contain an appreciable fraction of dehydroascorbic acid. The effects of sex, age, cigarette smoking, drugs, and physiological factors on vitamin C levels are better known for plasma than leukocytes. To realize the potential of leukocytes as measures of vitamin C status, continued work is needed in standardizing the methodology and interpretive guidelines and simplifying the technique for blood processing. The search for specific functional markers of vitamin C deficiency should continue. Candidate markers may involve pathways of carnitine or collagen metabolism, immunocompetence, or antioxidant defense.

Urinary hydroxyproline excretion and vitamin C status in healthy young men

The relationship between ascorbic acid status and the urinary excretion of hydroxyproline was examined in 11 healthy male subjects fed an ascorbic acid-deficient diet for 14 wk while in a metabolic unit. The diet provided 5 mg ascorbic acid/d and was supplemented with ascorbic acid to give intakes of 65 mg/d (2 wk), 5 mg/d (4 wk), 605 mg/d (3 wk), 5 mg/d (4 wk), and an average 375 mg/d (1 wk). The urinary excretion of hydroxyproline increased by an average of 16% and 30% after the first and second depletion periods, respectively, and decreased to baseline values after supplementation with normal or high doses of vitamin C. Significant (p less than 0.05) inverse correlations were found between urinary hydroxyproline and plasma, red cell, and leukocyte ascorbic acid. These results show that urinary hydroxyproline excretion increases during human vitamin C deficiency but that this effect is not strong enough to provide a reliable marker of mild vitamin C deficiency.

The prevalence of cardiovascular risk factors among elderly Chinese Americans

In 1981 to 1983, the nutrition and health status of 346 Chinese immigrants in Boston, Mass, aged 60 to 96 years was surveyed and analyzed for cardiovascular risk factors. These elderly Chinese were physically active and seldom obese and consumed a high-carbohydrate (57% of total energy intake), low-fat (24% of total energy intake), low-ascorbic acid (0.62 mmol/d) diet. Current cigarette smoking was common (39%) only in men, while alcoholism was rare in both sexes. Compared with elderly whites, they had lower mean blood pressure and blood levels of total, low-density lipoprotein, and high-density lipoprotein cholesterol, apolipoproteins A-I and B, and ascorbic acid. These characteristics resemble those of the urban population in mainland China, where hemorrhagic stroke is the major cause of cardiovascular mortality.

Biochemical markers for assessment of niacin status in young men: levels of erythrocyte niacin coenzymes and plasma tryptophan

Seven male subjects housed in a controlled metabolic unit for 80 d were fed diets containing amounts of niacin and tryptophan ranging from 6.1 to 32 niacin equivalents (NE) per day. Erythrocyte nicotinamide adenine dinucleotide (NAD) and nicotinamide nucleotide phosphate (NADP), activity of nicotinic acid mononucleotide phosphoribosyltransferase (NMNPRT), plasma tryptophan levels and the urinary excretion of organic acids were measured during dietary periods of low (6.1 or 10.1), adequate (19) and high (25 or 32) NE intake. With both low NE diets, NAD levels in erythrocytes decreased by approximately 70% and increased during repletion with an adequate NE diet. NADP levels remained relatively unchanged. Plasma tryptophan levels decreased by 40% and 10% in subjects ingesting diets of 6.1 and 10.1 NE/d, respectively. A daily 7.8-g leucine supplement during repletion was not associated with changes in plasma tryptophan levels or erythrocyte NAD and NADP levels at the end of the period. No changes in NMNPRT activity or organic acid excretion were found during the study. The results indicate that the erythrocyte NAD level may serve as a sensitive indicator for the assessment of niacin status. Also, a niacin index, the ratio of erythrocyte NAD to NADP, below 1.0 may identify subjects at risk of developing a niacin deficiency.

Lipofibroma of the superficial branch of the radial nerve

Lipofibromas of nerve are rare hamartomatous lesions almost exclusively involving the median nerve. To our knowledge, this is the first reported case of a lipofibroma involving a branch of the radial nerve.

Biochemical markers for assessment of niacin status in young men: urinary and blood levels of niacin metabolites

Biochemical markers of niacin status were studied in healthy young men fed 6.1 to 32 niacin equivalents (NE) per day over an 11-wk period while residing in a metabolic unit. Methylated metabolites of niacin, N1-methylnicotinamide (NMN) and N1-methyl-2-pyridone-5-carboxamide (2-pyr), in urine and plasma were determined during periods of low (6.1 or 10.1 NE per day), adequate (19 NE per day = 1 RDA) and high (25 or 32 NE per day) niacin intakes and after small test doses of nicotinamide. Urine excretion of less than 1.2 mg/d of either NMN or 2-pyr was a reliable indicator of subjects receiving the lowest intake of 6.1 NE/d, but the NMN metabolite was a better marker of subjects ingesting 10.1 NE/d. The ratio of 2-pyr/NMN in urine was not as good a measure of the 6.1 NE/d intake as the individual metabolite excretions and was not responsive to the 10.1 NE/d intake. Plasma niacin metabolites were generally not as reliable as urinary metabolites for identifying subjects receiving low niacin intakes, however, values for plasma 2-pyr dropped quickly and were eventually nondetectable. After a 1 RDA oral dose of nicotinamide, increases in urine and plasma 2-pyr levels above pre-dose baseline values were significantly decreased in subjects receiving low, as compared to adequate, niacin intake. A leucine supplement had no effect on the rate of repletion of niacin-deficient subjects nor on the level of methylated niacin metabolites in urine or plasma.

Ascorbic acid, HDL cholesterol, and apolipoprotein A-I in an elderly Chinese population in Boston

The relationships between plasma HDL cholesterol, apolipoprotein A-I, and plasma ascorbic acid were examined in 146 women and 92 men in a Chinese population in Boston, aged 60 and above. A significant partial correlation (r = 0.21, p = 0.015) between plasma ascorbic acid and plasma HDL cholesterol was observed among (predominantly nonsmoking) females after the effects of potentially confounding variables were taken into account. A similar relationship among 26 nonsmoking men was suggestive but inconclusive; there was no evidence of a relationship among 66 male smokers. The partial correlation between plasma apolipoprotein A-I and plasma ascorbic acid was marginally significant for women (r = 0.22, p = 0.057, n = 87) but was highly significant for men (r = 0.43, p = 0.007, n = 51). The correlation coefficient for men was highly dependent on smoking status, being 0.80 for those who never smoked and almost zero for current smokers.

Relationship of vitamin A and vitamin E intake to fasting plasma retinol, retinol-binding protein, retinyl esters, carotene, alpha-tocopherol, and cholesterol among elderly people and young adults: increased plasma retinyl esters among vitamin A-supplement users

We studied the relationships of supplemental and total vitamin A and supplemental vitamin E intake with fasting plasma biochemical indicators of vitamin A and vitamin E nutritional status among 562 healthy elderly people (aged 60-98 y) and 194 healthy young adult (aged 19-59 y) volunteers. All subjects were nonsmokers. For the young adults, plasma retinol was significantly greater in males than in females (p less than 0.01); retinol was not related to supplemental vitamin A intake for either group. Fasting plasma retinyl esters demonstrated a significant increase with vitamin A supplement use. For supplemental vitamin A intakes of 5001-10,000 IU/d, a 2.5-fold increase over nonusers in fasting plasma retinyl esters was observed for elderly people (p less than 0.05) and a 1.5-fold increase for young adults (p greater than 0.20). For elderly people, greater fasting plasma retinyl esters were associated with long-term vitamin A supplement use (greater than 5 y) and biochemical evidence of liver damage. Elderly people who take vitamin A supplements may be at increased risk for vitamin A overload.

Vitamin C status and nutrient interactions in a healthy elderly population

Vitamin C status and interactions with other nutrients were studied in 677 healthy, noninstitutionalized elderly people aged 60-98 y. Although 6% of the males and 3% of the females showed marginal vitamin C status (plasma ascorbic acid 11 to less than 23 mumol/L), only one person had a plasma ascorbic acid (AA) level less than 11 mumol/L. At all levels of total vitamin C intake, mean plasma AA levels were higher in females than males. Vitamin C supplement use was associated with generally higher blood levels of vitamins B-6, B-12, and E and folate in both sexes and with higher levels of retinol in females. However, after both age and the total dietary intake of the specific nutrient being examined were controlled for, plasma AA levels were significantly correlated only with plasma levels of vitamin E and folate in females.

Nutrient supplement use by healthy elderly

As part of a nutritional status survey of 691 non-institutionalized men and women aged 60 years and older, supplement use was reported by 45% of the males and 55% of the females. Supplement use was more prevalent in females than males at each age decade. Vitamins C and E were the most commonly used supplements. Mean dietary nutrient intakes were calculated from a 3-day food diary. The percentage of dietary intakes falling below 2/3 1980 Recommended Dietary Allowance (RDA) was comparable for users and non-users of supplements. Use of supplements markedly decreased the proportion of subjects with inadequate nutrient intake (using a 2/3 RDA criterion), particularly for vitamins B6, B12, and D, folic acid, and calcium. However, for both males and females, potentially excessive intake levels (10 times the RDA) of thiamin, vitamin A, and vitamin E supplementation were observed.

Vitamin A analogs as tests for liver vitamin A status in the rat

Two chlorinated retinol analogs (Ro 11-0503 and Ro 11-8284) were assayed in rat serum and correlated to retinol in liver. Rats were fed a retinol-free diet to deplete their liver stores, then repleted with 0.5, 1.0, 3.0, and 10.0 mg retinyl palmitate/kg diet. Rats were given intraperitoneal injections of the analog then killed after an additional week on the diets. Analogs were measured by HPLC. The relative abundance of both analogs in serum was inversely correlated with the amount of retinyl palmitate in the liver. Serum analog concentrations may be useful as indications of liver retinol stores.

Dietary intakes and biochemical indicators of nutritional status in an elderly, institutionalized population

A dietary and biochemical assessment of the nutritional status of 260 elderly men and women, 60-101 y (average 80.5 y), was conducted in 15 long-term-care facilities in the Boston area. Subjects were free of clinically apparent terminal or wasting illness. Nutrient intakes were comparable to those in a simultaneously studied free-living population as were most biochemical markers of nutrient status. Although no specific nutrient deficiencies were identified, blood levels of vitamin A and retinol-binding protein in males and of zinc in both sexes were lower in this institutionalized group than in the free-living subjects. Hematologic indices, albumin, prealbumin, and transferrin levels were also lower than in noninstitutionalized elderly populations. These differences may reflect the greater prevalence of chronic diseases and medication use in a long-term-care population. However, there is no evidence that institutionalization in itself leads to impairment of nutritional status.

Effect of varying ascorbic acid intakes on copper absorption and ceruloplasmin levels of young men

Intestinal copper absorption and blood measures of copper status were studied in healthy young men receiving varying intakes of ascorbic acid (AA) over 14 wk in a live-in nutrition suite. Copper absorption and retention were assessed by measuring absorption of a stable isotope of copper and total fecal copper during four AA intake periods: 2 wk x 65 mg AA/d, 4 wk x 5 mg/d, 3 wk x 605 mg/d and 4 wk x 5 mg/d. Measures of copper status were serum copper and serum ceruloplasmin determined by both enzymatic and immunochemical methods. Copper absorption, copper retention, total serum copper and the serum level of ceruloplasmin protein were not affected significantly by the changes in AA intake; however, the oxidase activity of serum ceruloplasmin was decreased an average of 21% during the high (605 mg/d) AA intake period. The results suggest that in adult men moderate supplemental intakes of AA reduce ceruloplasmin oxidase activity specifically but do not depress intestinal copper absorption or overall body copper status.

Biochemical indices of human vitamin C status

Biochemical indicators of ascorbic acid (AA) status were studied in eleven young adult males fed the same AA deficient diet for 14 wk in a live-in metabolic unit. Supplements of AA were added to the diet to give AA-intake periods of 65 mg/d (2 wk), 5 mg/d (4 wk), 605 mg/d (3 wk), 5 mg/d (4 wk), 605 mg/d (4 d), and 65 mg/d (3 d). Blood plasma, erythrocyte, and leukocyte AA levels all reflected AA intake, however, plasma AA showed less variability than red cell AA levels and was considerably easier to determine than leukocyte AA. Plasma AA values less than 0.40 mg/dL (23 mumol/L) reflected marginal AA status. The daily AA intake calculated to maintain plasma AA levels of at least 0.4 mg/dL (23 mumol/L) in healthy young men was 41 mg. The average AA intake estimated to maximize the total body pool was 138 mg/d. Urine and salivary AA levels were not useful indicators of AA status because urinary AA levels did not discriminate well between adequate and deficient AA intakes and salivary AA levels did not consistently reflect AA intake.

Protein nutriture of a group of free-living elderly

The adequacy of the protein intakes of elderly people without overt debilitating diseases was investigated on 691 free-living men and women divided into those aged 60-75 y and those greater than 75 y. In both age groups men and women had average protein intakes of 1.02-1.06 g/kg body weight, values well above the safe level of 0.75 g/kg recommended in a WHO/FAO/UNU report. Although plasma concentrations of albumin, prealbumin, and transferrin declined with age, these were not related to low intakes of protein by individual elderly people. Similarly, upper-arm muscle mass was not less in those elderly people at the lower end of the range of protein intakes. Thus in this population of overtly healthy elderly men and women, there was no evidence of protein deficiency in contrast to other surveys where elderly people with chronic diseases were included.

Experimental vitamin C depletion and supplementation in young men. Nutrient interactions and dental health effects

Biochemical indices of AA clearly showed that the young men in this study were brought into various states of AA depletion and repletion according to their dietary AA intakes. While previous studies have postulated that supplemental intakes of AA may adversely affect body status of vitamins B6 and B12, we found no changes in the B vitamin status of the young men receiving varying AA intakes. Moderate AA supplementation (605 mg/day) showed no antagonistic effect on markers of vitamins B6 and B12. Blood markers of fat-soluble vitamins A and E and iron status were not affected by AA intakes. The propensity of the gingiva to become inflamed or bleed on probing was reduced after normal (65 mg/day) AA intakes as compared to deficient (5 mg/day) intakes and upon supplementary (605 mg/day) AA intakes as compared to normal intakes. The results suggest that AA status may influence early stages of gingival inflammation and crevicular bleeding, and warrant further study of the relationship between AA and periodontal health.

The short and long term effect of gastric partitioning surgery on serum protein levels

The morbidly obese who undergo elective gastric partitioning surgery serve as models of surgical stress and subsequent severe protein calorie restriction. The short and long term effects of gastric partitioning surgery on circulating proteins and the specific micronutrients carried by the proteins were studied in 22 such patients (ages 23-56 years). Serum micronutrient values paralleled the levels of their carrier proteins. Mean concentrations of both short and long turnover proteins decreased significantly in the early postoperative period, whereas the acute phase reactant ceruloplasmin reached preoperative levels by the seventh postoperative day. Transthyretin and retinol binding protein remained depressed with long term reductions in protein and calorie intake, whereas ceruloplasmin and transferrin were somewhat less sensitive to prolonged protein-calorie restriction. Mean serum albumin, after an initial postoperative fall, rose to the baseline level by 1 month after surgery. Serum albumin levels remained within the normal range despite low protein and calorie intakes.