Vitamin D Status and Seasonal Variation among Danish Children and Adults: A Descriptive Study.

The aim of the present study was to describe vitamin D status and seasonal variation in the general Danish population. In this study, 3092 persons aged 2 to 69 years (2565 adults, 527 children) had blood drawn twice (spring and autumn) between 2012 and 2014. A sub-sample of participants had blood samples taken monthly over a year. Serum 25-hydroxyvitamin D (25(OH)D) concentrations were measured by liquid chromatography mass spectrometry, and information on supplement use was assessed from questionnaires. Seasonal variations in 25(OH)D concentrations were evaluated graphically and descriptively, and status according to age, sex, and supplement use was described. It was found that 86% of both adults and children were vitamin D-sufficient in either spring and or/autumn; however, many had a spring concentration below 50 nmol/L. A wide range of 25(OH)D concentrations were found in spring and autumn, with very low and very high values in both seasons. Among adults, women in general had higher median 25(OH)D concentrations than men. Furthermore, vitamin D supplement use was substantial and affected the median concentrations markedly, more so during spring than autumn. Seasonal variation was thus found to be substantial, and bi-seasonal measurements are vital in order to capture the sizable fluctuations in vitamin D status in this Nordic population.

Vitamin D status assessed by a validated HPLC method: within and between variation in subjects supplemented with vitamin D3.

OBJECTIVE: The aim of this study was to develop and validate a high-pressure liquid chromatography (HPLC) method for assessing vitamin D status as 25-hydroxyvitamin D(2) (S-25OHD(2)) and 25-hydroxyvitamin D(3) (S-25OHD(3)) in serum. MATERIAL AND METHODS: We assessed the within- and between-subject variation of vitamin D status in serum samples from four different dietary intervention studies in which subjects (n = 92) were supplemented with different doses of vitamin D(3) (5-12 microg/day) and for different durations (4-20 months). RESULTS: The HPLC method was applicable for 4.0-200 nmol S-25OHD/L, while the within-day and between-days variations were 3.8 % and 5.7 %, respectively. There was a concentration-dependent difference between results obtained by a commercial radioimmunoassay and results from the HPLC method of -5 to 20 nmol 25OHD/L in the range 10-100 nmol 25OHD/L. The between-subject variation estimated in each of the four human intervention studies did not differ significantly (p = 0.55). Hence, the pooled standard deviation was 15.3 nmol 25OHD(3)/L. In the studies with 6-8 samplings during 7-20 months of supplementation, the within-subject variation was 3.9-7.2 nmol 25OHD(3)/L, while vitamin D status was in the range 47-120 nmol/L. CONCLUSIONS: The validated HPLC method was applied in samples from human intervention studies in which subjects were supplemented with vitamin D(3). The estimated standard deviation between and within subjects is useful in the forthcoming decision on setting limits for optimal vitamin D status.

Effect of vitamin D supplementation on bone and vitamin D status among Pakistani immigrants in Denmark: a randomised double-blinded placebo-controlled intervention study.

Severe vitamin D deficiency is common among Muslim immigrants. The dose necessary to correct the deficiency and its consequence for bone health are not known for immigrants. The aim was to assess the effect of relatively low dosages of supplemental vitamin D on vitamin D and bone status in Pakistani immigrants. This 1-year-long randomised double-blinded placebo-controlled intervention with vitamin D3 (10 and 20 microg/d) included girls (10.1-14.7 years), women (18.1-52.7 years) and men (17.9-63.5 years) of Pakistani origin living in Denmark. The main endpoints were serum 25-hydroxyvitamin D (S-25OHD), parathyroid hormone, bone turnover markers and bone mass. The study showed that supplementation with 10 and 20 microg vitamin D3 per d increased S-25OHD concentrations similarly in vitamin D-deficient Pakistani women (4-fold), and that 10 microg increased S-25OHD concentrations 2-fold and 20 microg 3-fold in Pakistani men. S-25OHD concentrations increased at 6 months and were stable thereafter. Baseline S-25OHD concentrations tended to be lower in girls and women than in men; females achieved about 46 nmol/l and men 55 nmol/l after supplementation. Serum intact parathyroid hormone concentrations decreased at 6 months, but there was no significant effect of the intervention on bone turnover markers and dual-energy X-ray absorptiometry measurements of the whole body and lumbar spine.