Poor Status of Vitamin D: A Survey of Area With Lowest Sunlight Radiation in Sichuan, China.

Objective: Vitamin D plays an important role in bone and mineral metabolism. Ultraviolet B (UVB) is the primary determinant for vitamin D synthesis. However, population-based data of vitamin D status was sparse in areas with sunlight deprivation in China. This study aimed to assess serum 25-hydroxyvitamin D [25(OH)D] levels among adult women in Sichuan basin with the lowest sunlight radiation in China, and the associations with sunlight exposure and age. Methods: In the context of the same ethnicity, similar latitude and lifestyle in sunlight-limited basin and sunlight-abundant plateau, 1,057 women in basin and 337 in plateau aged 29-95 years were included in this study, from November 2012 to February 2013. Daily sunlight exposure duration of previous month was obtained using questionnaires. Serum 25(OH)D was measured by enzyme-linked immunosorbent assay. Results: The prevalence of vitamin D severe deficiency [25(OH)D <30 nmol/L] and deficiency [30 ≤ 25(OH)D <50 nmol/L] was significantly higher in basin than plateau (21.85% vs. 10.09%, and 59.32% vs. 40.36%; P<0.0001). Women from basin exhibited lower serum 25(OH)D levels than those from plateau (40.66 ± 15.62 vs. 52.54 ± 19.94 nmol/L, P<0.0001). In basin, women more than 50 years old had higher 25(OH)D than younger counterparts, and 25(OH)D level of these groups was not associated with sunlight exposure duration. While in plateau, women younger than 60 years old had higher 25(OH)D than the older women. Furthermore, for those younger groups, women with long sunlight exposure (≥3 h daily) had higher 25(OH)D concentration than those with short sunlight exposure (<3 h daily). Serum PTH was negatively associated with 25(OH)D in basin, but not in plateau. Conclusions: Alarmingly high prevalence of vitamin D deficiency was observed in women in sunlight-deprived basin in Sichuan. Only the vitamin D status of younger women from plateau with adequate solar radiation could benefit from sunlight exposure. Vitamin D supplementation and vitamin D-fortified food should be encouraged to improve vitamin D status for women living in sunlight-limited areas, or with old age.

[Association of Serum Vitamin D with Hand-grip Strength and Balance Ability: a Cross-sectional Study on Community-dwelling Women in Sichuan, China].

OBJECTIVE: To determine the relationship between serum levels of 25(OH)D and 1, 25(OH)2 D and the hand-grip strength and balance ability of women in Sichuan, China. METHODS: A cross-sectional study on a representative sample of 1 095 women aged 29-95 yr. in Sichuan Province was undertaken. Their hand-grip strength and balance ability were assessed using a hand-held dynamometer and the short physical performance battery (SPPB), respectively. The participants were divided into four groups according to the level of serum 25(OH)D: sufficient (>75 nmol/L), insufficient (51-75 nmol/L), deficiency (25-50 nmol/L), and serious deficiency (<25 nmol/L). General liner models were established to compare the differences of the four groups in balance ability. Logistic regression models were established to examine the associations of serum 25(OH)D and 1, 25(OH)2 D withhand-grip strength and physical performance. RESULTS: About 70.9% of the participants had vitamin D deficiency. Those with vitamin D insufficiency or deficiency were more likely to reside in a higher latitudinal area (P<0.001), spend less time in outdoor activities (P=0.013), and take less vitamin D supplements (P<0.001). Older women (≥65 years) had lower serum 25(OH)D (P=0.001) and were more likely to have ≤50 nmol/L 25(OH)D than their younger counterparts (74.6% vs. 68.9%, P=0.046). However, no significant age differences were found in serum 1, 25(OH)2 D. Serum levels of 25(OH)D and 1, 25(OH)2 D were not found to be associated with hand-grip strength and balance ability after adjusting for confounding factors. Hand-grip strength and balance ability decreased with age (OR=1.066, P<0.001; OR=1.111, P<0.001). Higher body mas was associated with higher hand-grip strength (OR=0.958, P<0.001). Higher serum albumin (OR=0.896, P=0.001) and longer walking time (OR=0.799, P=0.001) were associated with higher balance ability. CONCLUSION: Serum levels of 25(OH)D and 1, 25(OH)2D are not associated with hand-grip strength and balance ability.