Both significantly reduce the ability of the body to produce vitamin D. Sunlight plays an important role in vitamin D synthesis as most of it is made from exposure to the ultraviolet rays. However, a sunscreen with a SPF of 8 or higher effectively blocks the synthesis of vitamin D in skin. Lack of sunlight creates a similar problem in certain geographic locations, such as the northern regions of the country, as sun intensity is minimal during certain times of the year. The sunlight is just too weak during winter months to stimulate vitamin D production in the skin. The aging process decreases the amounts of vitamin D produced over time and the skin becomes less efficient at manufacturing it.
Vitamin D is a necessary nutrient, as it is needed for calcium absorption into bone.
If vitamin D stores are low, the body is only capable of absorbing 10 to 15 percent of all calcium consumed which leads to weak bones and a higher risk of debilitating fractures. Recommendations have been established to help serve as nutrition guidelines for specific age groups. Other suggestions for increasing vitamin D stores include staying outside for 10 to 15 minutes before applying sunscreen during the warm months and consider taking a daily multivitamin, which usually includes 400 IU of vitamin D during winter months. For adults older than 70 years and anyone with a diagnosis of vitamin D deficiency, a daily multivitamin plus a vitamin D supplement of 400 Ius, which totals 800 IUs of vitamin D, may be appropriate. If already taking a calcium supplement, look for one that also contains vitamin D. Supplementation of vitamin D should be carefully considered based on individual needs and discussed with a doctor as vitamin D could be toxic to the kidneys at levels exceeding 2,000 IUs per day.