(HOST) It's summer, the season of sunshine, so we're all getting plenty of vitamin D, the "sunshine vitamin", right? Well, maybe not, according to commentator Rachel Johnson.

(JOHNSON) Vitamin D is so critical to our health that nature designed a fail-safe way to obtain it: from the sun. Throughout history, exposure to the sun gave humans the vital doses needed to build bones and protect children against the characteristic bowed legs of rickets and adults from osteomalacia or softening of the bones.

But now, even in the summer months, we spend more time in-doors, in cars and behind computers. Americans drink much less milk than we did decades ago and when we do go outside we slather on sunscreen. So it's no coincidence that rickets, which was virtually wiped out until the 1990s, is making a comeback. Older people in hospitals and nursing homes are especially likely to lack the vitamin. In one study, fifty-seven percent of the elderly patients admitted to a Boston hospital were found to be vitamin D-deficient.

So how much vitamin D should you get? That question has been controversial ever since 1997 when the official recommendations for the vitamin were last updated. Many experts believed even then that the recommendations should be set much higher than they were - and now, that belief is growing. In a recent issue of the prestigious American Journal of Clinical Nutrition, 15 vitamin D experts from eight countries joined together to describe the urgent need for higher intakes of vitamin D. The evidence is mounting that vitamin D is important for much more than just bones; the vitamin seems to have a role in preventing some cancers, diabetes, arthritis and even multiple sclerosis.

For now the official recommendations for adequate intake of vitamin D range from two hundred to six hundred international units or IUs per day depending on your age. But there is growing agreement among experts that 1,000 IUs a day are needed for optimal vitamin D status. In fact, the Dietary Guidelines for Americans, the government's authoritative voice on what to eat to stay healthy, declared in 2005 that the elderly, people with dark skin and those exposed to insufficient sunlight like people who are housebound or in nursing homes need 1000 IUs daily. And in Canada, where sunlight can be especially scarce during the winter months and because it is nearly impossible to meet older people's vitamin D needs from food alone, health officials recommend that every adult over age fifty take a vitamin D pill containing four hundred IUs.

Aside from supplements, a few glasses of milk every day, a couple of servings of fatty fish weekly and an occasional egg yolk - along with fortified foods and perhaps a little sunshine - will go a long way toward sending old-time diseases like rickets back to ancient history where they belong. And, just maybe, help ward off modern-day scourges like cancer and diabetes in the future. Modern life may have made it harder to get the vitamin D we need, but luckily the solutions to this challenge are simple.

Nutritionist Rachel Johnson is Dean of the College of Agriculture and Life Sciences at UVM and an advisor to EatingWell magazine.