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Vitamin D status can be assessed by measuring concentrations of 25-hydroxyvitamin D (25(OH)D). Sunlight is the most important source of vitamin D and stimulates the production of vitamin D3 in the skin during the summer, depending on age, skin pigmentation, clothing style, and sunscreen use. Seasonal variation in serum 25(OH)D is between 10 and 20 nmol/L in adults and almost absent in nursing home residents. Sunscreen use decreases, but does not abolish, vitamin D production in the skin. Clothing style has a large influence on vitamin D production. Furthermore, vitamin D status can be improved by ingestion of fatty fish and the fortification of milk or orange juice. A high dietary calcium intake has a vitamin D-sparing effect, because it increases the half-life of 25(OH)D. A combination of sunlight exposure, nutrition, food fortification, and supplements is desirable to obtain sufficient vitamin D status in the population of most countries throughout the year. [ABSTRACT FROM AUTHOR]

Objective The prevalence of both low testosterone levels and depression increases with age. Currently, there is no consensus regarding the existence of an association. Our study analyses the cross-sectional association of testosterone levels with depressive symptoms and its prospective association with the development of incident depressive symptoms. Design Longitudinal population-based study; based on the data of the Longitudinal Aging Study Amsterdam (LASA) including 608 men aged ≥65 years (median age 75·6 years). Measurements Linear and logistic regression between total and free testosterone levels and depressive symptoms as measured by the Center of Epidemiologic Studies Depression (CES-D) scale, taking into account medical and lifestyle factors. Cox Proportional Hazards model was used to assess incident depressive symptoms. Results Unadjusted linear regression between square-root transformed CES-D scores and free testosterone levels showed a significant inverse association as a continuous variable (β = −0·10, P < 0·05), lowest quartile compared to highest (β = 0·12, P < 0·05) and with a threshold value of 170 pmol/l (β = 0·13, P < 0·05). The results remained significant for the group below threshold after adjustment for all confounders (β = 0·09, P < 0·05). Cox Proportional Hazards Model showed a decreased risk for incident depressive symptoms for men with higher free testosterone levels [HR = 0·997 CI (0·995–1·000)]. Men with the threshold value below 220 pmol/l were at increased risk of incident depressive symptoms [HR = 1·989 CI (1·173–3·374)]. Conclusions Free testosterone levels below 170 pmol/l are associated with depressive symptoms, while free testosterone levels below 220 pmol/l (lowest quintile of our population) predict the onset of depressive symptoms. [ABSTRACT FROM AUTHOR]