Plasma homocysteine as a risk factor for dementia and Alzheimer's disease

BACKGROUND

In cross-sectional studies, elevated plasma homocysteine levels have been associated with poor cognition and dementia. Studies of newly diagnosed dementia are required in order to establish whether the elevated homocysteine levels precede the onset of dementia or result from dementia-related nutritional and vitamin deficiencies.

METHODS

A total of 1092 subjects without dementia (667 women and 425 men; mean age, 76 years) from the Framingham Study constituted our study sample. We examined the relation of the plasma total homocysteine level measured at base line and that measured eight years earlier to the risk of newly diagnosed dementia on follow-up. We used multivariable proportional-hazards regression to adjust for age, sex, apolipoprotein E genotype, vascular risk factors other than homocysteine, and plasma levels of folate and vitamins B12 and B6.

RESULTS

Over a median follow-up period of eight years, dementia developed in 111 subjects, including 83 given a diagnosis of Alzheimer's disease. The multivariable-adjusted relative risk of dementia was 1.4 (95 percent confidence interval, 1.1 to 1.9) for each increase of 1 SD in the log-transformed homocysteine value either at base line or eight years earlier. The relative risk of Alzheimer's disease was 1.8 (95 percent confidence interval, 1.3 to 2.5) per increase of 1 SD at base line and 1.6 (95 percent confidence interval, 1.2 to 2.1) per increase of 1 SD eight years before base line. With a plasma homocysteine level greater than 14 micromol per liter, the risk of Alzheimer's disease nearly doubled.

CONCLUSIONS

An increased plasma homocysteine level is a strong, independent risk factor for the development of dementia and Alzheimer's disease.

Vitamin D deficiency and risk of cardiovascular disease

BACKGROUND

Vitamin D receptors have a broad tissue distribution that includes vascular smooth muscle, endothelium, and cardiomyocytes. A growing body of evidence suggests that vitamin D deficiency may adversely affect the cardiovascular system, but data from longitudinal studies are lacking.

METHODS AND RESULTS

We studied 1739 Framingham Offspring Study participants (mean age 59 years; 55% women; all white) without prior cardiovascular disease. Vitamin D status was assessed by measuring 25-dihydroxyvitamin D (25-OH D) levels. Prespecified thresholds were used to characterize varying degrees of 25-OH D deficiency (< 15 ng/mL, < 10 ng/mL). Multivariable Cox regression models were adjusted for conventional risk factors. Overall, 28% of individuals had levels < 15 ng/mL, and 9% had levels < 10 ng/mL. During a mean follow-up of 5.4 years, 120 individuals developed a first cardiovascular event. Individuals with 25-OH D < 15 ng/mL had a multivariable-adjusted hazard ratio of 1.62 (95% confidence interval 1.11 to 2.36, P=0.01) for incident cardiovascular events compared with those with 25-OH D > or = 15 ng/mL. This effect was evident in participants with hypertension (hazard ratio 2.13, 95% confidence interval 1.30 to 3.48) but not in those without hypertension (hazard ratio 1.04, 95% confidence interval 0.55 to 1.96). There was a graded increase in cardiovascular risk across categories of 25-OH D, with multivariable-adjusted hazard ratios of 1.53 (95% confidence interval 1.00 to 2.36) for levels 10 to < 15 ng/mL and 1.80 (95% confidence interval 1.05 to 3.08) for levels < 10 ng/mL (P for linear trend=0.01). Further adjustment for C-reactive protein, physical activity, or vitamin use did not affect the findings.

CONCLUSIONS

Vitamin D deficiency is associated with incident cardiovascular disease. Further clinical and experimental studies may be warranted to determine whether correction of vitamin D deficiency could contribute to the prevention of cardiovascular disease.

Long-term morbidity and mortality of overweight adolescents. A follow-up of the Harvard Growth Study of 1922 to 1935

BACKGROUND

Overweight in adults is associated with increased morbidity and mortality. In contrast, the long-term effect of overweight in adolescence on morbidity and mortality is not known.

METHODS

We studied the relation between overweight and morbidity and mortality in 508 lean or overweight adolescents 13 to 18 years old who participated in the Harvard Growth Study of 1922 to 1935. Overweight adolescents were defined as those with a body-mass index that on two occasions was greater than the 75th percentile in subjects of the same age and sex in a large national survey. Lean adolescents were defined as those with a body-mass index between the 25th and 50th percentiles. Subjects who were still alive were interviewed in 1988 to obtain information about their medical history, weight, functional capacity, and other risk factors. For those who had died, information on the cause of death was obtained from death certificates.

RESULTS

Overweight in adolescent subjects was associated with an increased risk of mortality from all causes and disease-specific mortality among men, but not among women. The relative risks among men were 1.8 (95 percent confidence interval, 1.2 to 2.7; P = 0.004) for mortality from all causes and 2.3 (95 percent confidence interval, 1.4 to 4.1; P = 0.002) for mortality from coronary heart disease. The risk of morbidity from coronary heart disease and atherosclerosis was increased among men and women who had been overweight in adolescence. The risk of colorectal cancer and gout was increased among men and the risk of arthritis was increased among women who had been overweight in adolescence. Overweight in adolescence was a more powerful predictor of these risks than overweight in adulthood.

CONCLUSIONS

Overweight in adolescence predicted a broad range of adverse health effects that were independent of adult weight after 55 years of follow-up.

Common genetic determinants of vitamin D insufficiency: a genome-wide association study

BACKGROUND

Vitamin D is crucial for maintenance of musculoskeletal health, and might also have a role in extraskeletal tissues. Determinants of circulating 25-hydroxyvitamin D concentrations include sun exposure and diet, but high heritability suggests that genetic factors could also play a part. We aimed to identify common genetic variants affecting vitamin D concentrations and risk of insufficiency.

METHODS

We undertook a genome-wide association study of 25-hydroxyvitamin D concentrations in 33 996 individuals of European descent from 15 cohorts. Five epidemiological cohorts were designated as discovery cohorts (n=16 125), five as in-silico replication cohorts (n=9367), and five as de-novo replication cohorts (n=8504). 25-hydroxyvitamin D concentrations were measured by radioimmunoassay, chemiluminescent assay, ELISA, or mass spectrometry. Vitamin D insufficiency was defined as concentrations lower than 75 nmol/L or 50 nmol/L. We combined results of genome-wide analyses across cohorts using Z-score-weighted meta-analysis. Genotype scores were constructed for confirmed variants.

FINDINGS

Variants at three loci reached genome-wide significance in discovery cohorts for association with 25-hydroxyvitamin D concentrations, and were confirmed in replication cohorts: 4p12 (overall p=1.9x10(-109) for rs2282679, in GC); 11q12 (p=2.1x10(-27) for rs12785878, near DHCR7); and 11p15 (p=3.3x10(-20) for rs10741657, near CYP2R1). Variants at an additional locus (20q13, CYP24A1) were genome-wide significant in the pooled sample (p=6.0x10(-10) for rs6013897). Participants with a genotype score (combining the three confirmed variants) in the highest quartile were at increased risk of having 25-hydroxyvitamin D concentrations lower than 75 nmol/L (OR 2.47, 95% CI 2.20-2.78, p=2.3x10(-48)) or lower than 50 nmol/L (1.92, 1.70-2.16, p=1.0x10(-26)) compared with those in the lowest quartile.

INTERPRETATION

Variants near genes involved in cholesterol synthesis, hydroxylation, and vitamin D transport affect vitamin D status. Genetic variation at these loci identifies individuals who have substantially raised risk of vitamin D insufficiency.

FUNDING

Full funding sources listed at end of paper (see Acknowledgments).

Vitamin status and intake as primary determinants of homocysteinemia in an elderly population

OBJECTIVE

To describe the distribution of plasma homocysteine concentrations in an elderly population and to analyze the relationship between homocysteine level and intake of vitamins and serum levels of vitamins that serve as coenzymes in homocysteine metabolism.

DESIGN

Cross-sectional analysis of homocysteine levels and vitamin blood levels and intake in elderly participants in the Framingham Study.

SETTING

Population-based cohort in Framingham, Mass.

PARTICIPANTS

A total of 1160 adult survivors, aged 67 to 96 years, from the original Framingham Heart Study cohort.

MAIN OUTCOME MEASURES

Plasma homocysteine concentration correlated with plasma folate, vitamin B12, pyridoxal-5'-phosphate (PLP), and oral intakes of these vitamins, and the contribution of these vitamins to the prevalence of elevated homocysteine in the population.

RESULTS

Homocysteine levels were positively correlated with age after controlling for vitamin concentrations. After controlling for age, sex, and levels of other vitamins, homocysteine exhibited a strong inverse association with plasma folate. When subjects were grouped by deciles of plasma folate, mean homocysteine was significantly higher in the lowest two folate deciles (15.6 and 13.7 mumol/L, respectively) than in the highest decile (11.0 mumol/L). Homocysteine demonstrated weaker, inverse associations with plasma vitamin B12 and PLP. Similar inverse associations were demonstrated between homocysteine and intakes of folate and vitamin B6, but not vitamin B12. Prevalence of high homocysteine (> 14 mumol/L) was 29.3% in this cohort, and was greatest among subjects with low folate status. Inadequate plasma concentrations of one or more B vitamins appear to contribute to 67% of the cases of high homocysteine.

CONCLUSIONS

These results indicate a strong association between homocysteine concentration and folate, vitamin B12, and vitamin B6 status, as well as age. It is possible that a substantial majority of the cases of high homocysteine in this older population can be attributed to vitamin status.

Multiple biomarkers for the prediction of first major cardiovascular events and death

BACKGROUND

Few investigations have evaluated the incremental usefulness of multiple biomarkers from distinct biologic pathways for predicting the risk of cardiovascular events.

METHODS

We measured 10 biomarkers in 3209 participants attending a routine examination cycle of the Framingham Heart Study: the levels of C-reactive protein, B-type natriuretic peptide, N-terminal pro-atrial natriuretic peptide, aldosterone, renin, fibrinogen, D-dimer, plasminogen-activator inhibitor type 1, and homocysteine; and the urinary albumin-to-creatinine ratio.

RESULTS

During follow-up (median, 7.4 years), 207 participants died and 169 had a first major cardiovascular event. In Cox proportional-hazards models adjusting for conventional risk factors, the following biomarkers most strongly predicted the risk of death (each biomarker is followed by the adjusted hazard ratio per 1 SD increment in the log values): B-type natriuretic peptide level (1.40), C-reactive protein level (1.39), the urinary albumin-to-creatinine ratio (1.22), homocysteine level (1.20), and renin level (1.17). The biomarkers that most strongly predicted major cardiovascular events were B-type natriuretic peptide level (adjusted hazard ratio, 1.25 per 1 SD increment in the log values) and the urinary albumin-to-creatinine ratio (1.20). Persons with "multimarker" scores (based on regression coefficients of significant biomarkers) in the highest quintile as compared with those with scores in the lowest two quintiles had elevated risks of death (adjusted hazard ratio, 4.08; P<0.001) and major cardiovascular events (adjusted hazard ratio, 1.84; P=0.02). However, the addition of multimarker scores to conventional risk factors resulted in only small increases in the ability to classify risk, as measured by the C statistic.

CONCLUSIONS

For assessing risk in individual persons, the use of the 10 contemporary biomarkers that we studied adds only moderately to standard risk factors.

Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) synthesizes 5-methyltetrahydrofolate, the major carbon donor in remethylation of homocysteine to methionine. A common MTHFR mutation, an alanine-to-valine substitution, renders the enzyme thermolabile and may cause elevated plasma levels of the amino acid homocysteine.

METHODS AND RESULTS

To assess the potential interaction between this mutation and vitamin coenzymes in homocysteine metabolism, we screened 365 individuals from the NHLBI Family Heart Study. Among individuals with lower plasma folate concentrations ( < 15.4 nmol/L), those with the homozygous mutant genotype had total fasting homocysteine levels that were 24% greater (P<.05) than individuals with the normal genotype. A difference between genotypes was not seen among individuals with folate levels > or = 15.4 nmol/L.

CONCLUSIONS

Individuals with thermolabile MTHFR may have a higher folate requirement for regulation of plasma homocysteine concentrations; folate supplementation may be necessary to prevent fasting hyperhomocysteinemia in such persons.

Association between plasma homocysteine concentrations and extracranial carotid-artery stenosis

BACKGROUND

Epidemiologic studies have identified hyperhomocysteinemia as a possible risk factor for atherosclerosis. We determined the risk of carotid-artery atherosclerosis in relation to both plasma homocysteine concentrations and nutritional determinants of hyperhomocysteinemia.

METHODS

We performed a cross-sectional study of 1041 elderly subjects (418 men and 623 women; age range, 67 to 96 years) from the Framingham Heart Study. We examined the relation between the maximal degree of stenosis of the extracranial carotid arteries (as assessed by ultrasonography) and plasma homocysteine concentrations, as well as plasma concentrations and intakes of vitamins involved in homocysteine metabolism, including folate, vitamin B12, and vitamin B6. The subjects were classified into two categories according to the findings in the more diseased of the two carotid vessels: stenosis of 0 to 24 percent and stenosis of 25 to 100 percent.

RESULTS

The prevalence of carotid stenosis of > or = 25 percent was 43 percent in the men and 34 percent in the women. The odds ratio for stenosis of > or = 25 percent was 2.0 (95 percent confidence interval, 1.4 to 2.9) for subjects with the highest plasma homocysteine concentrations (> or = 14.4 mumol per liter) as compared with those with the lowest concentrations (< or = 9.1 mumol per liter), after adjustment for sex, age, plasma high-density lipoprotein cholesterol concentration, systolic blood pressure, and smoking status (P < 0.001 for trend). Plasma concentrations of folate and pyridoxal-5'-phosphate (the coenzyme form of vitamin B6) and the level of folate intake were inversely associated with carotid-artery stenosis after adjustment for age, sex, and other risk factors.

CONCLUSIONS

High plasma homocysteine concentrations and low concentrations of folate and vitamin B6, through their role in homocysteine metabolism, are associated with an increased risk of extracranial carotid-artery stenosis in the elderly.

The effect of folic acid fortification on plasma folate and total homocysteine concentrations

BACKGROUND

In 1996, the Food and Drug Administration issued a regulation requiring all enriched grain products to be fortified with folic acid to reduce the risk of neural-tube defects in newborns. Fortification (140 microg per 100 g) began in 1996, and the process was essentially complete by mid-1997.

METHODS

To assess the effect of folic acid fortification on folate status, we measured plasma folate and total homocysteine concentrations (a sensitive marker of folate status) using blood samples from the fifth examination (January 1991 to December 1994) of the Framingham Offspring Study cohort for baseline values and the sixth examination (January 1995 to August 1998) for follow-up values. We divided the cohort into two groups on the basis of the date of their follow-up examination: the study group consisted of 350 subjects who were seen after fortification (September 1997 to March 1998), and the control group consisted of 756 subjects who were seen before fortification (January 1995 to September 1996).

RESULTS

Among the subjects in the study group who did not use vitamin supplements, the mean folate concentrations increased from 4.6 to 10.0 ng per milliliter (11 to 23 nmol per liter) (P<0.001) from the baseline visit to the follow-up visit, and the prevalence of low folate concentrations (<3 ng per milliliter [7 nmol per liter]) decreased from 22.0 to 1.7 percent (P< 0.001). The mean total homocysteine concentration decreased from 10.1 to 9.4 micromol per liter during this period (P<0.001), and the prevalence of high homocysteine concentrations (>13 micromol per liter) decreased from 18.7 to 9.8 percent (P<0.001). In the control group, there were no statistically significant changes in concentrations of folate or homocysteine.

CONCLUSIONS

The fortification of enriched grain products with folic acid was associated with a substantial improvement in folate status in a population of middle-aged and older adults.

A common mutation in the 5,10-methylenetetrahydrofolate reductase gene affects genomic DNA methylation through an interaction with folate status

DNA methylation, an essential epigenetic feature of DNA that modulates gene expression and genomic integrity, is catalyzed by methyltransferases that use the universal methyl donor S-adenosyl-l-methionine. Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate (5-methylTHF), the methyl donor for synthesis of methionine from homocysteine and precursor of S-adenosyl-l-methionine. In the present study we sought to determine the effect of folate status on genomic DNA methylation with an emphasis on the interaction with the common C677T mutation in the MTHFR gene. A liquid chromatography/MS method for the analysis of nucleotide bases was used to assess genomic DNA methylation in peripheral blood mononuclear cell DNA from 105 subjects homozygous for this mutation (T/T) and 187 homozygous for the wild-type (C/C) MTHFR genotype. The results show that genomic DNA methylation directly correlates with folate status and inversely with plasma homocysteine (tHcy) levels (P < 0.01). T/T genotypes had a diminished level of DNA methylation compared with those with the C/C wild-type (32.23 vs.62.24 ng 5-methylcytosine/microg DNA, P < 0.0001). When analyzed according to folate status, however, only the T/T subjects with low levels of folate accounted for the diminished DNA methylation (P < 0.0001). Moreover, in T/T subjects DNA methylation status correlated with the methylated proportion of red blood cell folate and was inversely related to the formylated proportion of red blood cell folates (P < 0.03) that is known to be solely represented in those individuals. These results indicate that the MTHFR C677T polymorphism influences DNA methylation status through an interaction with folate status.

Soft drink consumption and risk of developing cardiometabolic risk factors and the metabolic syndrome in middle-aged adults in the community

BACKGROUND

Consumption of soft drinks has been linked to obesity in children and adolescents, but it is unclear whether it increases metabolic risk in middle-aged individuals.

METHODS AND RESULTS

We related the incidence of metabolic syndrome and its components to soft drink consumption in participants in the Framingham Heart Study (6039 person-observations, 3470 in women; mean age 52.9 years) who were free of baseline metabolic syndrome. Metabolic syndrome was defined as the presence of > or = 3 of the following: waist circumference > or = 35 inches (women) or > or = 40 inches (men); fasting blood glucose > or = 100 mg/dL; serum triglycerides > or = 150 mg/dL; blood pressure > or = 135/85 mm Hg; and high-density lipoprotein cholesterol < 40 mg/dL (men) or < 50 mg/dL (women). Multivariable models included adjustments for age, sex, physical activity, smoking, dietary intake of saturated fat, trans fat, fiber, magnesium, total calories, and glycemic index. Cross-sectionally, individuals consuming > or = 1 soft drink per day had a higher prevalence of metabolic syndrome (odds ratio [OR], 1.48; 95% CI, 1.30 to 1.69) than those consuming < 1 drink per day. On follow-up (mean of 4 years), new-onset metabolic syndrome developed in 717 of 4033 participants (17.8%) consuming < 1 drink/day and in 433 of 2006 persons (21.6%) [corrected] consuming > or = 1 soft drink/day [corrected] Consumption of > or = 1 soft drink per day was associated with increased odds of developing metabolic syndrome (OR, 1.44; 95% CI, 1.20 to 1.74), obesity (OR, 1.31; 95% CI, 1.02 to 1.68), increased waist circumference (OR, 1.30; 95% CI, 1.09 to 1.56), impaired fasting glucose (OR, 1.25; 95% CI, 1.05 to 1.48), higher blood pressure (OR, 1.18; 95% CI, 0.96 to 1.44), hypertriglyceridemia (OR, 1.25; 95% CI, 1.04 to 1.51), and low high-density lipoprotein cholesterol (OR, 1.32; 95% CI 1.06 to 1.64).

CONCLUSIONS

In middle-aged adults, soft drink consumption is associated with a higher prevalence and incidence of multiple metabolic risk factors.

Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort

OBJECTIVE

The aim of this study was to examine the relation between carbohydrate-related dietary factors, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort.

RESEARCH DESIGN AND METHODS

We examined cross-sectional associations between carbohydrate-related dietary factors, insulin resistance, and the prevalence of the metabolic syndrome in 2,834 subjects at the fifth examination (1991-1995) of the Framingham Offspring Study. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated using the following formula (fasting plasma insulin x plasma glucose)/22.5. The metabolic syndrome was defined using the National Cholesterol Education Program criteria.

RESULTS

After adjustment for potential confounding variables, intakes of total dietary fiber, cereal fiber, fruit fiber, and whole grains were inversely associated, whereas glycemic index and glycemic load were positively associated with HOMA-IR. The prevalence of the metabolic syndrome was significantly lower among those in the highest quintile of cereal fiber (odds ratio [OR] 0.62; 95% CI 0.45-0.86) and whole-grain (0.67; 0.48-0.91) intakes relative to those in the lowest quintile category after adjustment for confounding lifestyle and dietary factors. Conversely, the prevalence of the metabolic syndrome was significantly higher among individuals in the highest relative to the lowest quintile category of glycemic index (1.41; 1.04-1.91). Total carbohydrate, dietary fiber, fruit fiber, vegetable fiber, legume fiber, glycemic load, and refined grain intakes were not associated with prevalence of the metabolic syndrome.

CONCLUSIONS

Whole-grain intake, largely attributed to the cereal fiber, is inversely associated with HOMA-IR and a lower prevalence of the metabolic syndrome. Dietary glycemic index is positively associated with HOMA-IR and prevalence of the metabolic syndrome. Given that both a high cereal fiber content and lower glycemic index are attributes of whole-grain foods, recommendation to increase whole-grain intake may reduce the risk of developing the metabolic syndrome.

Determinants of plasma total homocysteine concentration in the Framingham Offspring cohort

BACKGROUND

Established determinants of fasting total homocysteine (tHcy) concentration include folate and vitamin B-12 status, serum creatinine concentration, and renal function.

OBJECTIVE

Our objective was to examine the relation between known and suspected determinants of fasting plasma tHcy in a population-based cohort.

DESIGN

We examined the relations between fasting plasma tHcy concentrations and nutritional and other health factors in 1960 men and women, aged 28-82 y, from the fifth examination cycle of the Framingham Offspring Study between 1991 and 1994, before the implementation of folic acid fortification.

RESULTS

Geometric mean tHcy was 11% higher in men than in women and 23% higher in persons aged > or = 65 y than in persons aged < 45 y (P < 0.001). tHcy was associated with plasma folate, vitamin B-12, and pyridoxal phosphate (P for trend < 0.001). Dietary folate, vitamin B-6, and riboflavin were associated with tHcy among non-supplement users (P for trend < 0.01). The tHcy concentrations of persons who used vitamin B supplements were 18% lower than those of persons who did not (P < 0.001). tHcy was positively associated with alcohol intake (P for trend = 0.004), caffeine intake (P for trend < 0.001), serum creatinine (P for trend < 0.001), number of cigarettes smoked (P for trend < 0.001), and antihypertensive medication use (P < 0.001).

CONCLUSIONS

Our study confirmed, in a population-based setting, the importance of the known determinants of fasting tHcy and suggested that other dietary and lifestyle factors, including vitamin B-6, riboflavin, alcohol, and caffeine intakes as well as smoking and hypertension, influence circulating tHcy concentrations.

Folate and vitamin B-12 status in relation to anemia, macrocytosis, and cognitive impairment in older Americans in the age of folic acid fortification

BACKGROUND

Historic reports on the treatment of pernicious anemia with folic acid suggest that high-level folic acid fortification delays the diagnosis of or exacerbates the effects of vitamin B-12 deficiency, which affects many seniors. This idea is controversial, however, because observational data are few and inconclusive. Furthermore, experimental investigation is unethical.

OBJECTIVE

We examined the relations between serum folate and vitamin B-12 status relative to anemia, macrocytosis, and cognitive impairment (ie, Digit Symbol-Coding score < 34) in senior participants in the 1999-2002 US National Health and Nutrition Examination Survey.

DESIGN

The subjects had normal serum creatinine concentrations and reported no history of stroke, alcoholism, recent anemia therapy, or diseases of the liver, thyroid, or coronary arteries (n = 1459). We defined low vitamin B-12 status as a serum vitamin B-12 concentration < 148 pmol/L or a serum methylmalonic acid concentration > 210 nmol/L-the maximum of the reference range for serum vitamin B-12-replete participants with normal creatinine.

RESULTS

After control for demographic characteristics, cancer, smoking, alcohol intake, serum ferritin, and serum creatinine, low versus normal vitamin B-12 status was associated with anemia [odds ratio (OR): 2.7; 95% CI: 1.7, 4.2], macrocytosis (OR: 1.8; 95% CI: 1.01, 3.3), and cognitive impairment (OR: 2.5; 95% CI: 1.6, 3.8). In the group with a low vitamin B-12 status, serum folate > 59 nmol/L (80th percentile), as opposed to < or = 59 nmol/L, was associated with anemia (OR: 3.1; 95% CI: 1.5, 6.6) and cognitive impairment (OR: 2.6; 95% CI: 1.1, 6.1). In the normal vitamin B-12 group, ORs relating high versus normal serum folate to these outcomes were < 1.0 (P(interaction) < 0.05), but significantly < 1.0 only for cognitive impairment (0.4; 95% CI: 0.2, 0.9).

CONCLUSION

In seniors with low vitamin B-12 status, high serum folate was associated with anemia and cognitive impairment. When vitamin B-12 status was normal, however, high serum folate was associated with protection against cognitive impairment.

Homocysteine as a predictive factor for hip fracture in older persons

BACKGROUND

The increased prevalence of osteoporosis among people with homocystinuria suggests that a high serum homocysteine concentration may weaken bone by interfering with collagen cross-linking, thereby increasing the risk of osteoporotic fracture. We examined the association between the total homocysteine concentration and the risk of hip fracture in men and women enrolled in the Framingham Study.

METHODS

We studied 825 men and 1174 women, ranging in age from 59 to 91 years, from whom blood samples had been obtained between 1979 and 1982 to measure plasma total homocysteine. The participants in our study were followed from the time that the sample was obtained through June 1998 for incident hip fracture. Sex-specific, age-adjusted incidence rates of hip fracture were calculated for quartiles of total homocysteine concentrations. Cox proportional-hazards regression was used to calculate hazard ratios for quartiles of homocysteine values.

RESULTS

The mean (+/-SD) plasma total homocysteine concentration was 13.4+/-9.1 micromol per liter in men and 12.1+/-5.3 micromol per liter in women. The median duration of follow-up was 12.3 years for men and 15.0 years for women. There were 41 hip fractures among men and 146 among women. The age-adjusted incidence rates per 1000 person-years for hip fracture, from the lowest to the highest quartile for total homocysteine, were 1.96 (95 percent confidence interval, 0.52 to 3.41), 3.24 (0.97 to 5.52), 4.43 (1.80 to 7.07), and 8.14 (4.20 to 12.08) for men and 9.42 (5.72 to 13.12), 7.01 (4.29 to 9.72), 9.58 (6.42 to 12.74), and 16.57 (11.84 to 21.30) for women. Men and women in the highest quartile had a greater risk of hip fracture than those in the lowest quartile--the risk was almost four times as high for men and 1.9 times as high for women.

CONCLUSIONS

These findings suggest that the homocysteine concentration, which is easily modifiable by means of dietary intervention, is an important risk factor for hip fracture in older persons.

Adiposity, cardiometabolic risk, and vitamin D status: the Framingham Heart Study

OBJECTIVE

Because vitamin D deficiency is associated with a variety of chronic diseases, understanding the characteristics that promote vitamin D deficiency in otherwise healthy adults could have important clinical implications. Few studies relating vitamin D deficiency to obesity have included direct measures of adiposity. Furthermore, the degree to which vitamin D is associated with metabolic traits after adjusting for adiposity measures is unclear.

RESEARCH DESIGN AND METHODS

We investigated the relations of serum 25-hydroxyvitamin D (25[OH]D) concentrations with indexes of cardiometabolic risk in 3,890 nondiabetic individuals; 1,882 had subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) volumes measured by multidetector computed tomography (CT).

RESULTS

In multivariable-adjusted regression models, 25(OH)D was inversely associated with winter season, waist circumference, and serum insulin (P < 0.005 for all). In models further adjusted for CT measures, 25(OH)D was inversely related to SAT (-1.1 ng/ml per SD increment in SAT, P = 0.016) and VAT (-2.3 ng/ml per SD, P < 0.0001). The association of 25(OH)D with insulin resistance measures became nonsignificant after adjustment for VAT. Higher adiposity volumes were correlated with lower 25(OH)D across different categories of BMI, including in lean individuals (BMI <25 kg/m(2)). The prevalence of vitamin D deficiency (25[OH]D <20 ng/ml) was threefold higher in those with high SAT and high VAT than in those with low SAT and low VAT (P < 0.0001).

CONCLUSIONS

Vitamin D status is strongly associated with variation in subcutaneous and especially visceral adiposity. The mechanisms by which adiposity promotes vitamin D deficiency warrant further study.

Flavonoid intake and cardiovascular disease mortality in a prospective cohort of US adults

BACKGROUND

Flavonoids are plant-based phytochemicals with cardiovascular protective properties. Few studies have comprehensively examined flavonoid classes in relation to cardiovascular disease mortality.

OBJECTIVE

We examined the association between flavonoid intake and cardiovascular disease (CVD) mortality among participants in a large, prospective US cohort.

DESIGN

In 1999, a total of 38,180 men and 60,289 women in the Cancer Prevention Study II Nutrition Cohort with a mean age of 70 and 69 y, respectively, completed questionnaires on medical history and lifestyle behaviors, including a 152-item food-frequency questionnaire. Cox proportional hazards modeling was used to calculate multivariate-adjusted hazard RRs and 95% CIs for associations between total flavonoids, 7 flavonoid classes, and CVD mortality.

RESULTS

During 7 y of follow-up, 1589 CVD deaths in men and 1182 CVD deaths in women occurred. Men and women with total flavonoid intakes in the top (compared with the bottom) quintile had a lower risk of fatal CVD (RR: 0.82; 95% CI: 0.73, 0.92; P-trend = 0.01). Five flavonoid classes-anthocyanidins, flavan-3-ols, flavones, flavonols, and proanthocyanidins-were individually associated with lower risk of fatal CVD (all P-trend < 0.05). In men, total flavonoid intakes were more strongly associated with stroke mortality (RR: 0.63; 95% CI: 0.44, 0.89; P-trend = 0.04) than with ischemic heart disease (RR: 0.90; 95% CI: 0.72, 1.13). Many associations appeared to be nonlinear, with lower risk at intakes above the referent category.

CONCLUSIONS

Flavonoid consumption was associated with lower risk of death from CVD. Most inverse associations appeared with intermediate intakes, suggesting that even relatively small amounts of flavonoid-rich foods may be beneficial.

Whole-grain intake is favorably associated with metabolic risk factors for type 2 diabetes and cardiovascular disease in the Framingham Offspring Study

BACKGROUND

The influence of whole grains on cardiovascular disease risk may be mediated through multiple pathways, eg, a reduction in blood lipids and blood pressure, an enhancement of insulin sensitivity, and an improvement in blood glucose control.

OBJECTIVE

The objective was to examine the association between diets rich in whole- or refined-grain foods and several metabolic markers of disease risk in the Framingham Offspring Study cohort.

DESIGN

Whole-grain intake and metabolic risk markers were assessed in a cross-sectional study of 2941 subjects.

RESULTS

After adjustment for potential confounding factors, whole-grain intake was inversely associated with body mass index (: 26.9 in the lowest and 26.4 in the highest quintile of intake; P for trend = 0.06), waist-to-hip ratio (0.92 and 0.91, respectively; P for trend = 0.005), total cholesterol (5.20 and 5.09 mmol/L, respectively; P for trend = 0.06), LDL cholesterol (3.16 and 3.04 mmol/L, respectively; P for trend = 0.02), and fasting insulin (205 and 199 pmol/L, respectively; P for trend = 0.03). There were no significant trends in metabolic risk factor concentrations across quintile categories of refined-grain intake. The inverse association between whole-grain intake and fasting insulin was most striking among overweight participants. The association between whole-grain intake and fasting insulin was attenuated after adjustment for dietary fiber and magnesium.

CONCLUSION

Increased intakes of whole grains may reduce disease risk by means of favorable effects on metabolic risk factors.

Short sleep duration and dietary intake: epidemiologic evidence, mechanisms, and health implications

Links between short sleep duration and obesity, type 2 diabetes, hypertension, and cardiovascular disease may be mediated through changes in dietary intake. This review provides an overview of recent epidemiologic studies on the relations between habitual short sleep duration and dietary intake in adults from 16 cross-sectional studies. The studies have observed consistent associations between short sleep duration and higher total energy intake and higher total fat intake, and limited evidence for lower fruit intake, and lower quality diets. Evidence also suggests that short sleepers may have irregular eating behavior deviating from the traditional 3 meals/d to fewer main meals and more frequent, smaller, energy-dense, and highly palatable snacks at night. Although the impact of short sleep duration on dietary intake tends to be small, if chronic, it may contribute to an increased risk of obesity and related chronic disease. Mechanisms mediating the associations between sleep duration and dietary intake are likely to be multifactorial and include differences in the appetite-related hormones leptin and ghrelin, hedonic pathways, extended hours for intake, and altered time of intake. Taking into account these epidemiologic relations and the evidence for causal relations between sleep loss and metabolism and cardiovascular function, health promotion strategies should emphasize improved sleep as an additional factor in health and weight management. Moreover, future sleep interventions in controlled studies and sleep extension trials in chronic short sleepers are imperative for establishing whether there is a causal relation between short sleep duration and changes in dietary intake.

A temporal association between folic acid fortification and an increase in colorectal cancer rates may be illuminating important biological principles: a hypothesis

Nationwide fortification of enriched uncooked cereal grains with folic acid began in the United States and Canada in 1996 and 1997, respectively, and became mandatory in 1998. The rationale was to reduce the number of births complicated by neural tube defects. Concurrently, the United States and Canada experienced abrupt reversals of the downward trend in colorectal cancer (CRC) incidence that the two countries had enjoyed in the preceding decade: absolute rates of CRC began to increase in 1996 (United States) and 1998 (Canada), peaked in 1998 (United States) and 2000 (Canada), and have continued to exceed the pre-1996/1997 trends by 4 to 6 additional cases per 100,000 individuals. In each country, the increase in CRC incidence from the prefortification trend falls significantly outside of the downward linear fit based on nonparametric 95% confidence intervals. The statistically significant increase in rates is also evident when the data for each country are analyzed separately for men and women. Changes in the rate of colorectal endoscopic procedures do not seem to account for this increase in CRC incidence. These observations alone do not prove causality but are consistent with the known effects of folate on existing neoplasms, as shown in both preclinical and clinical studies. We therefore hypothesize that the institution of folic acid fortification may have been wholly or partly responsible for the observed increase in CRC rates in the mid-1990s. Further work is needed to definitively establish the nature of this relationship. In the meantime, deliberations about the institution or enhancement of fortification programs should be undertaken with these considerations in mind.

Nonfasting plasma total homocysteine levels and stroke incidence in elderly persons: the Framingham Study

BACKGROUND

Total homocysteine levels are associated with arteriosclerotic outcomes.

OBJECTIVE

To determine whether total homocysteine levels predict incident stroke in elderly persons.

DESIGN

Prospective population-based cohort study with 9.9 years of follow-up.

SETTING

Framingham, Massachusetts.

PATIENTS

1947 Framingham Study participants (1158 women and 789 men; mean age +/- SD, 70 +/- 7 years).

MEASUREMENTS

Baseline total homocysteine levels and 9.9-year stroke incidence.

RESULTS

The quartiles of nonfasting total homocysteine levels were as follows: quartile 1, 4.13 to 9.25 micromol/L; quartile 2, 9.26 to 11.43 micromol/L; quartile 3, 11.44 to 14.23 micromol/L; quartile 4, 14.24 to 219.84 micromol/L. During follow-up, 165 incident strokes occurred. In proportional hazards models adjusted for age, sex, systolic blood pressure, diabetes, smoking, and history of atrial fibrillation and coronary heart disease, relative risk (RR) estimates comparing quartile 1 with the other three quartiles were as follows: quartile 2 compared with quartile 1--RR, 1.32 (95% CI, 0.81 to 2.14); quartile 3 compared with quartile 1--RR, 1.44 (CI, 0.89 to 2.34); quartile 4 compared with quartile 1--RR, 1.82 (CI, 1.14 to 2.91). The linear trend across the quartiles was significant (P < 0.001).

CONCLUSION

Nonfasting total homocysteine levels are an independent risk factor for incident stroke in elderly persons.

Cytokines, insulin-like growth factor 1, sarcopenia, and mortality in very old community-dwelling men and women: the Framingham Heart Study

BACKGROUND

Aging is associated with increased production of catabolic cytokines, reduced circulating levels of insulin-like growth factor 1 (IGF-1), and acceleration of sarcopenia (loss of muscle with age). We hypothesized that these factors are independently linked to mortality in community-dwelling older persons.

METHODS

We examined the relation of all-cause mortality to peripheral blood mononuclear cell production of inflammatory cytokines (tumor necrosis factor alpha [TNF-alpha], interleukin 1 beta, interleukin 6), serum interleukin 6 and IGF-1, and fat-free mass and clinical status in 525 ambulatory, free-living participants in the Framingham Heart Study.

RESULTS

Of the 525 subjects (aged 72 to 92 years at baseline), 122 (23%) died during 4 years of follow-up. After adjusting for age, sex, comorbid conditions, smoking, and body mass index, mortality was associated with greater cellular production of TNF-alpha (hazard ratio [HR] = 1.27 per log(10) difference in ng/mL; 95% confidence interval [CI]: 1.00 to 1.61; P = 0.05) and higher serum interleukin 6 levels (HR = 1.30 per log(10) difference in pg/mL; 95% CI: 1.04 to 1.63]; P = 0.02), but not with higher serum IGF-1 levels (HR = 0.70 per log(10) difference in pg/mL; 95% CI: 0.49 to 0.99; P = 0.04). In a subset of 398 subjects (55 deaths) in whom change in fat-free mass index during the first 2 years was measured, less loss of fat-free mass and greater IGF-1 levels were associated with reduced mortality during the next 2 years.

CONCLUSION

Greater levels or production of the catabolic cytokines TNF-alpha and interleukin 6 are associated with increased mortality in community-dwelling elderly adults, whereas IGF-1 levels had the opposite effect.

The 1298A-->C polymorphism in methylenetetrahydrofolate reductase (MTHFR): in vitro expression and association with homocysteine

A common mutation in methylenetetrahydrofolate reductase (MTHFR), 677C-->T, is associated with reduced enzyme activity, a thermolabile enzyme and mild hyperhomocysteinemia, a risk factor for vascular disease. Recently, a second common mutation (1298A-->C; glutamate to alanine) was reported, but this mutation was suggested to increase homocysteine only in individuals who carried the bp677 variant. To evaluate the functional consequences of this mutation, we performed site-directed mutagenesis and in vitro expression. For in vivo assessment of clinical impact, we examined the 1298A-->C genotypes and plasma homocysteine in 198 individuals from the NHLBI Family Heart Study that had previously been assessed for the 677 substitution. Site-directed mutagenesis of the human cDNA was performed to generate enzymes containing each of the two mutations, as well as an enzyme containing both substitutions. Enzyme activity and thermolability were assessed in bacterial extracts. The activity of the wild-type cDNA was designated as 100%; mutant enzymes containing the 1298 and 677 mutations separately had 68% (+/-5.0) and 45% (+/-10.8), respectively, of control activity while the enzyme containing both mutations had 41% (+/-12.8) of control activity. The 1298 mutation was not associated with a thermolabile enzyme. In the Family Heart Study, fasting homocysteine was significantly higher (P<0.05) in individuals heterozygous for both substitutions, compared to individuals who carried only the 677C-->T variant. This study suggests that two variants in MTHFR should be assessed as genetic risk factors for hyperhomocysteinemia.

Serum total homocysteine concentrations in the third National Health and Nutrition Examination Survey (1991-1994): population reference ranges and contribution of vitamin status to high serum concentrations

BACKGROUND

The concentration of circulating total homocysteine is a sensitive marker of inadequate folate and vitamin B12 status. Elevated homocysteine concentrations are associated with an increased risk for vascular disease.

OBJECTIVE

To identify reference ranges for serum total homocysteine concentration in U.S. residents and quantify the contribution of circulating vitamin concentrations to high homocysteine concentrations.

DESIGN

Cross-sectional prevalence study.

SETTING

United States.

PATIENTS

A nationally representative sample of 3563 male participants and 4523 female participants 12 years of age or older who participated in the third National Health and Nutrition Examination Survey.

MEASUREMENTS

Reference ranges (5th and 95th percentiles) for the total homocysteine concentration were defined among participants who were folate- and vitamin B12-replete and had normal creatinine concentrations. A high total homocysteine concentration was defined as one that exceeded the sex-specific 95th percentile for the reference sample (participants 20 to 39 years of age). The population attributable risk percentage was calculated to determine the contribution of low folate (<11 nmol/L) and vitamin B12 (<185 pmol/L) concentrations to a high homocysteine concentration.

RESULTS

Reference ranges for serum total homocysteine concentration increased with age; these ranges were 4.3 to 9.9 micromol/L for male participants and 3.3 to 7.2 micromol/L for female participants 12 to 19 years of age and from 5.9 to 15.3 micromol/L for men and 4.9 to 11.6 micromol/L for women 60 years of age or older. A high homocysteine concentration was defined as at least 11.4 micromol/L for male participants and at least 10.4 micromol/L for female participants. Approximately two thirds of the cases of high homocysteine concentrations were associated with low vitamin concentrations.

CONCLUSIONS

Upper reference limits for the serum total homocysteine concentration increased with age and were higher for male participants than for female participants at all ages. In most cases, high homocysteine concentrations were associated with low serum vitamin concentrations.