Be it sweater or swimsuit season, a daily dose of the "sunshine vitamin" may significantly shrink your risk of disease and death.

And although the stuff naturally occurs in your skin when exposed to the sun, you should faithfully pop a vitamin D supplement as well, because you need more D than Mother Nature -- or your diet -- can probably provide.

A Vital Vitamin
Vitamin D may be particularly helpful in thwarting cancer and arterial diseases. (Get more disease-deterring advice by simply filling out this questionnaire.) Why? It's not entirely clear yet. But these conditions rely on cell proliferation to do their damage, and vitamin D may help slow down that process. (Try these top 10 tips for beating Major Agers.)

Making D Work for You
So how can you tap into the sunshine vitamin's benefits? A bit of safe sun and some D-rich foods will boost your blood levels -- but only so much. (Look up food sources with this tool.) To gain the life-extending effects researchers recently identified, you'll need a daily supplement, too. Either form you find at your drugstore, vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol), will do the trick.

Are you getting enough vitamin D, calcium, and other antiaging nutrients? Take this assessment and find out.

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Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Autier, P., Gandini, S., Archives of Internal Medicine 2007 Sep 10;167(16):1730-1737.