Effect of Season on 25-OH Vitamin D in Serum of Rhesus Monkeys Housed in Puerto Rico.

OBJECTIVE: Vitamin D blood levels have been shown to be partially dependent upon season in temperate climates, however, this same evaluation has not yet been reported in fully tropical climates. Herein, we assessed the vitamin D levels in the blood of Rhesus monkeys housed at the Puerto Rico Caribbean Primate Research Center collected in the island's "summer"(May-October) and "winter" (November-April) months. MATERIALS AND METHODS: In 2006 through 2014, repeated measurements of blood samples were collected from 5 Rhesus monkeys (IACUC-approved) during "summer" and "winter" months to assess 25-OH vitamin D, determined via HPLC. UV-B and UV-A (KJ/m2/day) were measured using a ground based radiometer for these time periods. A paired t-test and a multilevel mixed- effect model approach was performed for data analysis. RESULTS: The difference of the mean serum values of 25-OH vitamin D between seasons showed lower levels during "winter" than "summer" months. About 23% of the variance in levels can be attributed to difference between the monkeys. The means of UV-B and UV-A, as a proxy for sunlight intensity, were greater (over the entire study interval) during the "summer" as opposed to "winter" months (p < 0.001). CONCLUSION: Vitamin D levels were substantially higher in the "summer" rather than the "winter" months. This observation implies that even in fully tropical regions, such as Puerto Rico, time of year can have an influence on vitamin D status. While comparable studies have not been undertaken in humans, it would not be unreasonable to suggest that similar results would be obtained should such a study be done.

Effect of Housing Type on 25 OH Vitamin D in Serum of Rhesus Monkeys.

OBJECTIVE: Vitamin D status is primarily dependent upon sun exposure and dietary sources, however genetic, cultural, and environmental factors can have a modulating role in the measured amount. One under-reported factor is the effect of regular living quarters on the degree of sun exposure. Herein, we assess vitamin D status in the blood of Rhesus monkeys (Macaca mulatta) housed in high amounts of sunlight (corn-cribs), medium sunlight (corrals with shaded areas), and minimal sunlight (quarantine cages). METHODS: Fifty-five male Rhesus monkeys, aged 1 to 31 years were housed in varying amounts of sun exposure at the Caribbean Primate Research Center. Serum was collected and analyzed for 25 OH Vitamin D which is the preferred metabolite for determination of Vitamin D using High Performance Liquid Chromatography (HPLC). RESULTS: 25 OH Vitamin D levels in blood were significantly greater in corn-cribhoused monkeys than in corral or quarantine-housed animals (p > 0.01 and p > 0.001 respectively). Significant differences of serum levels were not found when ages of animals housed in the same environment were compared. CONCLUSION: Monkeys housed in a tropical environment with the greatest amount of exposure to sunlight maintain the highest serum levels of 25 OH vitamin D independent of age. These findings emphasize the importance of documenting the environment in which subjects typically spend their time when Vitamin D results are interpreted.