Oestrogen has no short-term effect on intestinal strontium absorption in healthy postmenopausal women

Determinants of vitamin D status in young adults: influence of lifestyle, sociodemographic and anthropometric factors

BACKGROUND

Very few studies have investigated the determinants of circulating 25-hydroxyvitamin D (25[OH]D) in young adults (18-25 years old) using a set of variables that include lifestyle, sociodemographic, and anthropometric data. Our aim was to investigate the association between these variables and vitamin D status in a sample of untreated young adults.

METHODS

A total of 738 young adults were enrolled in a (June cross-sectional study 2012 to May 2014) and were recruited from educational institutions in the Copenhagen area. For multivariate logistic regression subjects was categorized based on 25[OH]D in serum into; vitamin D sufficiency (S-25[OH]D > 50 nmol/L), vitamin D insufficiency (25 nmol/L ≤ S-25[OH]D ≤ 50 nmol/L), vitamin D deficiency (S-25[OH]D < 25 nmol/L). Information on lifestyle factors and education was obtained by self-reported questionnaires.

RESULTS

700 subjects with a valid measurement of S-25[OH]D and a completed questionnaire was analysed. 238 had vitamin D insufficiency, 135 had vitamin D deficiency of which 13 had severe vitamin D deficiency (S-25[OH]D < 12.5 nmol/L). The relative risk (RR) for vitamin D deficiency was highest for men 2.09 (1.52, 2.87); obese subjects 2.00 (1.27, 3.15); smokers 1.33 (1.02, 1.73); subjects who exercised 0-½ hours a week 1.88 (1.21, 2.94); and subjects who consumed fast food once a week 1.59 (1.05, 2.43). The relative risk was significantly lower for subjects who were studying for a Bachelor's degree (0.40 (0.23, 0.68). For vitamin D insufficiency, the highest RR was again for men 1.31 (1.06, 1.61); obese subjects 1.57 (1.17, 2.11); and subjects who exercised 0-½ hours a week 1.51 (1.11, 2.06).

CONCLUSION

In this study of young adults, vitamin D deficiency was highly prevalent. Modifiable factors such as smoking, maintenance of normal BMI, and physical activity are all potential targets for interventional trials to determine the causal order; such knowledge would be useful in improving S-25[OH]D in young adults. The small group with severe vitamin D deficiency warrants increased attention.

25-Hydroxyvitamin D level does not reflect intestinal calcium absorption: an assay using strontium as a surrogate marker

There is conflicting evidence as to the optimal serum 25-hydroxyvitamin D [25(OH)D] concentration for intestinal calcium absorption (Abs-Ca). Our purpose was to assess the relationship between vitamin D status and Abs-Ca in postmenopausal women. Fifty volunteers with low bone mass were grouped according to their serum 25(OH)D concentration as follows: mild deficient, <50 nmol/L (DEF) and sufficient, ≥75 nmol/L (SUF). The subjects were submitted to an oral strontium overload test to assess their Abs-Ca. Fasting blood samples were obtained to perform the relevant hormonal and biochemical tests. After the subjects received the test solution, blood samples were drawn at 30, 60, 120, and 240 min to determine the strontium concentrations. Abs-Ca was indirectly expressed as the area under the serum strontium concentration curve (AUC). A repeated measures ANOVA was performed to determine the differences among the groups. Pearson's correlation and multiple linear regression analysis were used to study the associations between the variables. The mean 25(OH)D and 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations differed between the groups (SUF vs. DEF) as follows: 98.7 ± 18.2 vs. 38.4 ± 8.5 nmol/L (p < 0.001) and 36.2 ± 10.2 vs. 24.9 ± 4.6 pg/mL (p < 0.001), respectively. There was no statistically significant difference between the groups for parathyroid hormone and AUC. Only 1,25(OH)2D influenced the strontium absorption in the last 2 h of the test. In the studied population, no correlation between levels of 25(OH)D and Abs-Ca was found. Only 1,25(OH)2D influenced Abs-Ca as measured by a strontium absorption test.

Sr and Fe relationship with hormone replacement therapy and bone mineral density

BACKGROUND

We determined blood strontium (Sr) and iron (Fe) concentrations and their relationship with bone mineral density (BMD) and some biochemical parameters in premenopausal and postmenopausal women without or with hormone replacement therapy (HRT).

METHODS

Blood Sr and Fe concentrations, BMD, follicle stimulating hormone (FSH), 17beta-estradiol (E2), creatinine, albumin, blood calcium and alkaline phosphatase activity were determined in premenopausal and postmenopausal women without or with HRT (mean ages: 47, 59, and 57 y, respectively).

RESULTS

Blood Sr (microg/l) and Fe (mg/l) concentrations in premenopausal (31.65+/-2.96 and 496.05+/-14.37) and postmenopausal women without (28.85+/-2.48 and 525.27+/-8.56) or with (25.98+/-2.73 and 535.77+/-17.57) HRT were not significantly different. BMD L1-L4 and BMD femur (g/cm2) were significantly higher in premenopausal women (1.05+/-0.02 and 0.84+/-0.02) when compared both to postmenopausal women without (0.90+/-0.03 and 0.75+/-0.02) and with (0.93+/-0.03 and 0.73+/-0.01) HRT. However, BMD had no relationship with blood metal concentrations. E2 concentrations were lower in postmenopausal women without HRT, while FSH concentrations were higher in both postmenopausal groups (p<0.05).

CONCLUSIONS

Physiological whole blood Sr and Fe concentrations had no significant effect in BMD and other biochemical parameters in pre and postmenopausal women. However, BMD was negatively influenced by FSH concentrations and associated with age.

Vitamin D Supplementation in Older Women

BACKGROUND

The purpose of this study was to determine if vitamin D supplementation, 400-800 IU daily, could effectively treat vitamin D deficiency and insufficiency over 3 months.

METHODS

To test this hypothesis, we conducted a cross-sectional survey followed by a 3-month, open-label run-in phase prior to a randomized clinical trial. We enrolled 573 community-dwelling women age 65 or older, 373 of whom completed the run-in phase. All women received a daily multivitamin containing 400 IU of vitamin D and one to two calcium supplements containing 200 IU of vitamin D. We assessed bone mineral metabolism (including 25-hydroxyvitamin D and parathyroid hormone), markers of bone turnover, and bone mineral density.

RESULTS

Of the 553 screened participants who had baseline vitamin D levels available, 16% had vitamin D deficiency (serum vitamin D < 10 ng/ml) and 48% had vitamin D insufficiency (serum vitamin D between 10 and 20 ng/ml). Only 36% of participants had normal vitamin D levels (serum vitamin D > or = 20 ng/ml). Baseline vitamin D intake was negatively associated with serum parathyroid hormone (r = -0.29, p <.0001), and not associated with bone mineral density or bone resorption. Vitamin D deficiency was associated with decreased physical activity and slower gait. Of the 373 women who completed the run-in phase and received treatment with a multivitamin and vitamin D-containing calcium supplement, vitamin D deficiency decreased from 16% at baseline to 0% at 3 months, and vitamin D insufficiency decreased from 48% at baseline to 20% at 3 months (p <.001).

CONCLUSIONS

We conclude that vitamin D deficiency and insufficiency, which are common among ambulatory, community-dwelling elderly women, can be normalized in 80% of patients over 3 months with vitamin D supplementation of 400-800 IU/d.

Circulating Vitamin D Metabolites, Polymorphism in Vitamin D Receptor, and Colorectal Adenoma Risk

Objective: Vitamin D is a potential agent for the prevention of colorectal cancer possibly through mechanisms mediated by the vitamin D receptor (VDR). We investigated the association of circulating vitamin D metabolites and a genetic variant of the VDR gene with advanced colorectal adenoma, a precursor lesion of colorectal cancer. Methods: Cases with advanced adenoma of the distal large bowel and gender- and ethnicity-matched controls with a negative sigmoidoscopy were randomly selected from participants in the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial. Genotype analysis of the VDR TaqI polymorphism was completed on 763 cases and 774 controls. Serum levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] were measured in a subset of 394 cases and 397 controls. Results: Serum levels of 25(OH)D were inversely associated with advanced adenoma risk in women but not in men. Comparing those in the highest quintile with those in the lowest quintile, the risk for advanced adenoma decreased by 73% in women [odds ratio (OR) = 0.27, 95% confidence interval (95% CI) = 0.11–0.69; P for trend = 0.0002], while the risk did not decrease in men (OR = 1.10, 95% CI = 0.60–2.05; P for trend = 0.85). In women, 25(OH)D levels were significantly higher in current users of hormone replacement therapy (HRT) than in former or never HRT users. Neither serum 1,25(OH)2D nor VDR TaqI genotype was associated with advanced adenoma risk. Conclusion: Higher serum 25(OH)D levels were associated with decreased adenoma risk. Serum 1,25(OH)2D and VDR TaqI genotype were not associated with adenoma risk.

The influence of estradiol and diet on small intestinal glucose transport in ovariectomized rats

Although gender differences exist for intestinal absorption of nutrients and drugs, the possible role estradiol may play in modulating nutrient transport has not been established. Therefore, small intestine glucose transport was measured 1 week after administering estradiol to ovariectomized rats fed diets high in carbohydrate (C) or protein (P). Rats treated with estradiol ate 21% less (P<0.05) and lost body mass (7%; P<0.05) but did not have smaller intestines. Administration of estradiol increased rates of glucose transport, but only when the rats were fed the C diet. These findings indicate that estradiol causes a disconnect between food intake and the dimensions and nutrient transport capacities of the small intestine. Furthermore, the responses to estradiol are influenced by diet composition, are not of the same magnitude for rats and dogs, and can be predicted to affect systemic availability of nutrients and drugs.

Effect of estrogen on intestinal strontium absorption in postmenopausal women

OBJECTIVES

there is considerable uncertainty about the underlying cause of decreased intestinal calcium absorption that occurs in postmenopausal women. In a previous study, estrogen treatment did not result in an increased intestinal calcium absorption using strontium as a marker. A possible explanation could be that the calcium/strontium load given to the women was too high ( approximately 600 mg Ca), which might result in an insensitive test with respect to the possible stimulation of active strontium transport by estrogen. Therefore, the purpose of this study was to reinvestigate the effect of estrogen on active intestinal strontium absorption using a load of 2.5 mmol of strontium only.

METHODS

the effect of estrogen on intestinal strontium absorption was measured in eight normal postmenopausal women. The study included two baseline strontium absorption tests, which were performed with an interval of 10 days for calculating the within subject variation (SER). Thereafter the effect of 2 months of estrogen treatment on intestinal strontium absorption was assessed. Fractional absorption (FC(240)) and the area under the concentration time curve (AUC) 4 h after an oral strontium load of 2.5 mmol were calculated.

RESULTS

the within subject SER of FC(240) and AUC(0-240) were 2.3+/-0.76 and 1.2+/-0.41, respectively. FC(240) and AUC(0-240) of strontium were unchanged after treatment with estrogen.

CONCLUSIONS

in normal postmenopausal women, we did not find a modulating effect of short-term treatment with a (supra) physiological dose of estrogen on intestinal calcium absorption as measured by the strontium absorption test.

The multifunctional properties and characteristics of vitamin D-binding protein

In recent years, our understanding of the many physiological, biochemical, and molecular functions and attributes of vitamin D-binding protein (DBP) has seen exciting and significant advances. Since its identification in 1959, many important functions of this abundant serum protein have been discovered. These range from the transport of vitamin D metabolites to possible roles in the immune system and host defense. With these discoveries, many questions regarding the biology of DBP have been raised and many remain to be answered. Our current understanding of the classic and less-recognized activities of DBP is discussed here.

Strontium as a Marker for Intestinal Calcium Absorption: The Stimulatory Effect of Calcitriol

Background: Intestinal strontium absorption is becoming accepted as a clinical and diagnostic tool for assessing intestinal calcium absorption in humans. However, little is known about whether intestinal strontium absorption, like that of calcium, is stimulated by calcitriol in healthy humans.

Methods: The effect of calcitriol on intestinal strontium absorption was measured in eight healthy men, ages 20–60 years. Before administration of calcitriol, two tests were performed with an interval of 10 days for calculating the within-subject variation (SER). Before the third test, 0.5 μg of calcitriol was given twice daily for 3 days. In each test, the fractional strontium absorption (Fc240) and the area under the concentration-time curve (AUC0–240) 4 h after an oral strontium load of 2.5 mmol were calculated.

Results: The within-subject SER of Fc240 and AUC0–240 was 1.7 ± 0.7 and 0.83 ± 0.1, respectively. The stimulatory effect of calcitriol on Fc240 and AUC0–240 was 35% (21.8 ± 2.0 to 28.8 ± 2.4; P = 0.003) and 61% (8.97 ± 0.97 to 14.4 ± 1.3 mmol · L−1 · min; P = 0.001), respectively.

Conclusions: Although the reproducibility of AUC0–240 and its sensitivity to calcitriol were better than those of Fc240, the Fc240 of strontium is preferred for a clinical test because of its simplicity, requiring only two instead of five blood samples.