Opposing actions of methylxanthines and dibutyryl cyclic AMP on 1,25 dihydroxyvitamin D3 production and calcium fluxes in isolated chick renal tubules

Higher intakes of dietary caffeine are associated with 25-hydroxyvitamin D deficiency

Low serum 25-hydroxyvitamin D [25(OH)D] levels remain a challenge worldwide. While some in vitro studies show a caffeine-induced decrease in vitamin D receptor expression, there is a paucity of research to define the extent of caffeine intake on 25(OH)D levels. Therefore, we aimed to associate dietary caffeine intake with 25(OH)D deficiency through a recognized dataset. Using data collected from the 2005-2006 National Health and Nutrition Examination Survey (NHANES), 25(OH)D levels and dietary caffeine intake were extracted from 13134 individuals (30-47 years, interquartile range). We used one-way ANOVA and chi-square tests for quantitative and qualitative variables, respectively, and performed multivariate logistic regression for four models to assess the odds ratio (OR) of 25(OH)D deficiency (<20 ng/ml or <50 nmol/L) based on quartiles of dietary caffeine intake. Both crude and multivariable models detected higher OR for 25(OH)D deficiency according to the highest intakes of caffeine (15.8±9.5, 51.9±11.9, and 177±156 mg/d) when compared to the reference category (2.19±1.04 mg/d), in which the OR in the highest category of caffeine intake was 1.24 (95% CI: 1.12 to 1.37) and 1.48 (95% CI: 1.16 to 1.78) for the crude model and the most complete multivariable analysis (adjustment for age, sex, race, body mass index, smoking, physical activity, occupation, energy intake, protein intake, and fat intake), respectively. In conclusion, higher dietary intakes of caffeine were associated with 25(OH)D deficiency in a representative sample of the American population, but further investigation is warranted to determine causation.

Tea and coffee consumption in relation to vitamin D and calcium levels in Saudi adolescents

BACKGROUND

Coffee and tea consumption was hypothesized to interact with variants of vitamin D-receptor polymorphisms, but limited evidence exists. Here we determine for the first time whether increased coffee and tea consumption affects circulating levels of 25-hydroxyvitamin D in a cohort of Saudi adolescents.

METHODS

A total of 330 randomly selected Saudi adolescents were included. Anthropometrics were recorded and fasting blood samples were analyzed for routine analysis of fasting glucose, lipid levels, calcium, albumin and phosphorous. Frequency of coffee and tea intake was noted. 25-hydroxyvitamin D levels were measured using enzyme-linked immunosorbent assays.

RESULTS

Improved lipid profiles were observed in both boys and girls, as demonstrated by increased levels of HDL-cholesterol, even after controlling for age and BMI, among those consuming 9-12 cups of coffee/week. Vitamin D levels were significantly highest among those consuming 9-12 cups of tea/week in all subjects (p-value 0.009) independent of age, gender, BMI, physical activity and sun exposure.

CONCLUSION

This study suggests a link between tea consumption and vitamin D levels in a cohort of Saudi adolescents, independent of age, BMI, gender, physical activity and sun exposure. These findings should be confirmed prospectively.

Caffeine and the calcium economy revisited

We report an analysis of data from 560 calcium balance studies carried out on 190 women aged 34.8-69.3 years at the time of study. The main purposes were to confirm a previously observed association between caffeine intake and calcium balance, and to attribute the association, if possible, to specific component(s) of balance. We found a caffeine relationship such that for every 6 fl oz (177.5 ml) serving of caffeine-containing coffee, calcium balance was more negative by 0.114 mmol/day (4.6 mg/day) (P < 0.001). The relationship was localized to the input side of the balance equation, and both of its components (i.e. calcium intake and calcium absorption efficiency) were independently and inversely associated with caffeine intake. There was no evidence that the putative caffeine effect is confined to, or is greater among, subjects with low calcium intakes or those who are older or estrogen-deprived. The magnitude of the negative effect of caffeine on calcium balance suggests that it can be offset by increasing calcium intake by about 1 mmol (40 mg) for every 177.5 ml serving of caffeine-containing coffee.

Differential effect of caffeine administration on calcium and vitamin D metabolism in young and adult rats

Since coffee drinking may lead to a worsening of calcium balance in humans, we studied the serial changes of serum calcium, PTH, 1,25-dihydroxyvitamin D (1,25(OH)2D) and calcium balance in young and adult rats after daily administration of caffeine for 4 weeks. In the young rats, there was an increase in urinary calcium and endogenous fecal calcium excretion after four days of caffeine administration that persisted for the duration of the experiment. Serum calcium decreased on the fourth day of caffeine administration and then returned to control levels. In contrast, the serum PTH and 1,25(OH)2D remained unchanged initially, but increased after 2 weeks of caffeine administration. The intestinal absorption coefficient of calcium remained unchanged, instead of declining gradually as observed in the young control group. This finding suggests that the intestinal absorption of calcium was stimulated by the increase in 1,25(OH)2D production after chronic administration of caffeine. In the adult rat group, an increase in the urinary calcium and endogenous fecal calcium excretion and serum levels of PTH was found after caffeine administration. However, the serum 1,25(OH)2D levels and intestinal absorption coefficient of calcium remained the same as in the adult control group. A decrease in the net balance of calcium occurred as a result of increased calcium excretion. The current study, using an animal model, supports the suggestion that chronic administration of caffeine could lead to negative calcium balance when there is an impaired ability to increase the efficiency of calcium absorption. Such a situation exists in elderly human subjects, since they have a reduced capacity to synthesize 1,25(OH)2D.