|MadSci Network: Medicine|
Daniel: Good Questions! Youíre righ,t sunscreen does block the skinís ability to produce Vitamin D. The SPF 8 prevents 95% of your skinís production of vitamin D, while the SPF 30 blocks 100%. Your second question involves a lot of variables which include: where you live, your skin coloration (do you sunburn or not), time of the day and season of the year.
Northern climates are less likely to have enough sun exposure to provide year-round Vit. D. The winter angle of the sun markedly limits the amount of UV-B radiation that can reach the earthís surface. Although, if you make enough Vit. D during the summer, this can be stored in your body fat and utilized in the winter. Older folks usually canít make enough during the summer.
Recommendations for sun exposure of the hands, face and arms should include: no sunscreen, 2 or 3 times a week for 50-70% LESS sun than would cause you to sunburn. I.e. if you "burn" after 30, do the above for 5-10 minutes only.
Vitamin D is available in fortified milk, I don't know if Japan fortifies its milk. You might read the label. Also, many multivitamins have Vit. D as a component. There are very few "other foods that have vitamin D" as a component. If you decide to supplement new daily recommendations are for 400Iu for adults 51-70, and 600Iu for the 71+. A quart of milk/ daily may provide 400-600Iu. Donít over do the supplements as Vitamin D can cause liver toxicity and a release of too much calcium from the bone, the latter ironic since that is what we need vitamin D for- to help with calcium absorption.
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