Vitamin D: A steroid vitamin which promotes the intestinal absorption and metabolism of calcium and phosphorus. Under normal conditions of sunlight exposure, no dietary supplementation is necessary because sunlight promotes adequate vitamin D synthesis in the skin. Deficiency can lead to bone deformity ( rickets ) in children and bone weakness (osteomalacia) in adults. Vitamin D comes from the diet (eggs, fish, and dairy products) and is produced in the skin. Skin production of the active form of vitamin D depends on exposure to sunlight. Active people living in sunny regions produce most of the vitamin D they need from their skin. In less sunny climes the skin production of vitamin D is markedly diminished in the winter months, especially among the elderly and the housebound. In that population, vitamin D supplements become important. Vitamin D deficiency among the elderly is quite common in the US. In a study of hospitalized patients in a general medical ward, vitamin D deficiency was detected in 57% of the patients. An estimated 50% of elderly women consume far less vitamin D in their diet than recommended. The Food and Nutrition Board of the Institute of Medicine has recommended the following as an adequate vitamin D intake: 200 IU daily for people 19-50 years old; 400 International Units (IU) daily for those 51-70 years old; and 600 IU daily for those 71 years and older. An average multivitamin tablet contains 400 IU of vitamin D. Therefore, taking a multivitamin a day should help provide the recommended amount of vitamin D. The new recommended daily allowance (RDA), as set in 2010, is based on age, as follows: for those 1-70 years of age, 600 IU daily; for those 71 years and older, 800 IU daily; and for pregnant and lactating women, 600 IU daily. The IOM further recommended that serum 25(OH)D levels of 20ng/mL (= 50 nmol/L) is adequate, and levels > 50ng/mL (= 125 nmol/L) could have potential adverse effects As to children, the National Academy of Sciences and American Academy of Pediatrics have recommended that all infants, including those who are exclusively breastfed, have a minimum intake of 200 International Units (IU) of vitamin D per day beginning during the first 2 months of life. In addition, it is recommended that an intake of 200 IU of vitamin D per day be continued throughout childhood and adolescence, because adequate sunlight exposure is not easily determined for a given individual.
The male reproductive tract has been identified as a target tissue for vitamin D, and previous data suggest an association of 25-hydroxyvitamin D [25(OH)D] with testosterone levels in men. We therefore aimed to evaluate whether vitamin D supplementation influences testosterone levels in men. Healthy overweight men undergoing a weight reduction program who participated in a randomized controlled trial were analyzed for testosterone levels. The entire study included 200 nondiabetic subjects, of whom 165 participants (54 men) completed the trial. Participants received either 83 μg (3,332 IU) vitamin D daily for 1 year (n = 31) or placebo (n =2 3). Initial 25(OH)D concentrations were in the deficiency range (< 50 nmol/l) and testosterone values were at the lower end of the reference range (- nmol/l for males aged 20-49 years) in both groups. Mean circulating 25(OH)D concentrations increased significantly by nmol/l in the vitamin D group, but remained almost constant in the placebo group. Compared to baseline values, a significant increase in total testosterone levels (from ± nmol/l to ± nmol/l; p < ), bioactive testosterone (from ± nmol/l to ± nmol/l; p = ), and free testosterone levels (from ± nmol/l to ± nmol/l; p = ) were observed in the vitamin D supplemented group. By contrast, there was no significant change in any testosterone measure in the placebo group. Our results suggest that vitamin D supplementation might increase testosterone levels. Further randomized controlled trials are warranted to confirm this hypothesis.