The lack of vitamin D is a major changeable factor involved in the pathophysiology of osteoporosis. Since the major source for this hormone is its cutaneous synthesis via ultraviolet radiation (UVR), we studied the serum level of 25-hydroxyvitamin D (25OHD) in 250 free-living elderly people (79.1 years old) from a subtropical region according to the UVR incidence and its correlations with parathormone (PTH) and ionized calcium. UVR and 25OHD differed according to the season of the year (P<0.001), with greater radiation in the summer and less in the winter, whereas the 25OHD peak and nadir occurred in autumn and spring, respectively. The highest 25OHD mean was 67.2 nmol/l, and the lowest was 29.1 nmol/l corresponding, respectively, to the measure of the month subsequent to the one of most and least sunlight incidence. Clustered by season, the correlation between UVR and 25OHD for the following seasons was r=0.98 and between the PTH and 25OHD of corresponding seasons, r=-0.95. Vitamin D deficiency occurred in 15.4% of patients, insufficiency in 41.9% and secondary hyperparathyroidism in 55%. In conclusion, we found a seasonal variation in 25OHD levels that strongly correlated with the PTH levels when separated by the seasons of the year. The 25OHD levels correlated with the UVR of the previous quarter, requiring no less than 30 days for serum changes arising from exposure to or deprivation of UVR to be observed. The prevalence of vitamin D deficiency/insufficiency found was greater than expected, even when compared to countries exposed to less solar irradiation. Thus, measures to encourage greater sun exposure and food enrichment policies should also be considered.

The range of 25-hydroxyvitamin D (25OHD) concentration was determined in a young healthy population based on bone metabolism parameters and environmental and behavioral aspects. We studied 121 healthy young volunteers (49 men, 72 women) living in São Paulo (23º 34' south latitude) belonging to three occupational categories: indoor workers (N = 28), medical school students (N = 44), and resident physicians (N = 49). Fasting morning blood samples were collected once from each volunteer from August 2002 to February 2004, and 25OHD, total calcium, albumin, alkaline phosphatase, phosphorus, creatinine, intact parathyroid hormone, osteocalcin, and type I collagen carboxyterminal telopeptide were measured. Data are reported as means ± SD. Mean subject age was 24.7 ± 2.68 years and mean 25OHD level for the entire group was 78.7 ± 33.1 nM. 25OHD levels were lower (P < 0.05) among resident physicians (67.1 ± 27.0 nM) than among students (81.5 ± 35.8 nM) and workers (94.0 ± 32.6 nM), with the last two categories displaying no difference. Parathyroid hormone was higher (P < 0.05) and osteocalcin was lower (P < 0.05) among resident physicians compared to non-physicians. Solar exposure and frequency of beach outings showed a positive association with 25OHD (P < 0.001), and summer samples presented higher results than winter ones (97.8 ± 33.5 and 62.9 ± 23.5 nM, respectively). To define normal levels, parameters such as occupational activity, seasonality and habits related to solar exposure should be taken into account. Based on these data, we considered concentrations above 74.5 nM to be desired optimal 25OHD levels, which were obtained during the summer for 75% of the non-physicians.