BackgroundVitamin D insufficiency is highly prevalent. Most of the studies concerning vitamin D status were generated from countries situated at temperate latitudes. It is less clear what the extent of vitamin D insufficiency is in countries situated in the tropics and how geographical regions within country would affect vitamin D status. In the present study, we investigated vitamin D status in Thais according to geographical regions and other risk factors.MethodsSubjects consisted of 2,641 adults, aged 15 - 98 years, randomly selected from the Thai 4th National Health Examination Survey (2008-9) cohort. Serum 25 hydroxyvitamin D were measured by liquid chromatography/tandem mass spectrometry. Data were expressed as mean ± SE.ResultsSubjects residing in Bangkok, the capital city of Thailand, had lower 25(OH)D levels than other parts of the country (Bangkok, central, northern, northeastern and southern regions: 64.8 ± 0.7, 79.5 ± 1.1, 81.7 ± 1.2, 82.2 ± 0.8 and 78.3 ± 1.3 nmol/L, respectively; p < 0.001). Within each region, except for the northeastern part of the country, subjects living inside municipal areas had lower circulating 25(OH)D (central, 77.0 ± 20.9 nmol/L vs 85.0 ± 22.1 nmol/L, p < 0.001; north 79.3 ± 22.1 nmol/L vs 86.8 ± 21.8 nmol/L, p < 0.001; northeast 84.1 ± 23.3 nmol/L vs 87.3 ± 20.9 nmol/L, p = 0.001; south, 76.6 ± 20.5 nmol/L vs 85.2 ± 24.7 nmol/L, p < 0.001). Overall, the prevalence of vitamin D insufficiency was 64.6%, 46.7%, and 33.5% in Bangkok, municipal areas except Bangkok, and outside municipal area in other parts of the country, respectively. In addition, the prevalence of vitamin D insufficiency according to geographical regions was 43.1%, 39.1%, 34.2% and 43.8% in the central, north, northeast and south, respectively. After controlling for covariates in multiple linear regression analysis, the results showed that low serum 25(OH)D levels were associated with being female, younger age, living in urban and Bangkok.ConclusionsVitamin D insufficiency is common and varies across geographical regions in Thailand.

Vitamin D status assessed by serum 25-hydroxyvitamin D levels (25(OH)D) has been shown to be inversely associated with insulin resistance. The underlying basis for such association is less clear. In the present study, we assessed the prevalence of inadequate vitamin D levels and its relationship to glucose tolerance status and circulating adiponectin in healthy Thai population. The cohort of 246 subjects was classified into two groups according to 75 g oral glucose tolerance test (OGTT) results. There were 86 subjects and 160 subjects in normal glucose tolerance group (NGT) and abnormal glucose tolerance group (AGT), respectively. Anthropometric variables were recorded for each individual. Fasting blood samples were assayed for 25(OH)D, adiponectin, glucose, and insulin levels. Insulin resistance (HOMA-IR) and insulin secretion index (HOMA-B) were calculated by the homeostasis model assessment. Pearson and partial correlation analyses were performed. There were 35 males and 211 females with a mean age of 62.4 +/- 7.2 years in this study. The mean levels of 25(OH)D were 21.4 +/- 6.6 ng/ml. The prevalence of vitamin D deficiency defined by 25(OH)D levels less than 20 ng/ml and vitamin D inadequacy defined by 25(OH)D levels less than 30 ng/ml were 44.3 and 91.9%, respectively. The mean levels of 25(OH)D obtained from samples collected in the rainy season (19.4 +/- 4.6 ng/ml) were significantly lower than those collected in the winter (22.6 +/- 8.3 ng/ml) and summer period (23.1 +/- 4.6 ng/ml). AGT subjects had slightly lower average 25(OH)D levels than the NGT group (21.0 +/- 6.8 vs. 22.1 +/- 6.2 ng/ml, P = 0.09). 25(OH)D levels were positively associated with adiponectin levels (r = 0.20, P< 0.05) and negatively associated with HOMA-IR and BMI (r = -0.22, P < 0.01 and r = -0.22, P < 0.01, respectively) only in AGT subjects. An independent association between 25(OH)D and adiponectin levels was demonstrated after controlling for BMI (r = 0.17, P < 0.05). High prevalence of vitamin D inadequacy and seasonal variation of vitamin D status are found in Thai population. We demonstrated an association between insufficient vitamin D status and lower circulating adiponectin in subjects with abnormal glucose tolerance independently of adiposity which may indicate the role of adiponectin as a link between vitamin D status and insulin resistance.

BackgroundIt is not known whether genetic variation in the vitamin D binding protein (DBP) influences 25-hydroxyvitamin D levels [25(OH)D] after vitamin D supplementation. We aimed to investigate the changes of total 25(OH)D, 25(OH)D3 and 25(OH)D2 in a Thai cohort, according to type of vitamin D supplement (vitamin D3 or D2) and DBP genotype, after receiving vitamin D3 or D2 for 3 months.MethodsThirty-nine healthy subjects completed the study. All subjects received 400 IU of either vitamin D3 or D2, plus a calcium supplement, every day for 3 months. Total serum 25(OH)D, 25(OH)D3 and 25(OH)D2 were measured by LC-MS/MS. Individual genotyping of rs4588 in the DBP gene was performed using real-time PCR.ResultsVitamin D3 supplementation of 400 IU/d increased 25(OH)D3 significantly (+16.2 ± 4.2 nmol/L, p <0.001). Vitamin D2 (400 IU/d) caused increased 25(OH)D2 levels (+22.0 ± 2.11 nmol/L, p <0.001), together with a decrease of 25(OH)D3 (−14.2 ± 2.0 nmol/L, p <0.001). At 3 month, subjects in vitamin D3 group tended to have higher total 25(OH)D levels than those in vitamin D2 (67.8 ± 3.9 vs. 61.0 ± 3.0 nmol/L; p = 0.08). Subjects were then classified into two subgroups: homozygous for the DBP rs4588 C allele (CC), and the rest (CA or AA). With D3 supplementation, subjects with CA or AA alleles had significantly less increase in 25(OH)D3 and total 25(OH)D when compared with those with the CC allele. However, no difference was found when the supplement was vitamin D2.ConclusionGenetic variation in DBP (rs4588 SNP) influences responsiveness to vitamin D3 but not vitamin D2.