For years, the message about the sun was simple —- avoid it. Slather on sunscreen. Wear a hat and long-sleeved shirts. The sun was your foe —- wrinkling your skin, or worse, causing skin cancer. The new message emerging? Maybe we went a little too far. As in SPF 70 too far.

Very few foods are naturally rich in vitamin D, and most Americans rely on limited sun exposure and fortified foods, such as milk and cereal to get their daily dose of the sunshine vitamin. As a result, many people are falling short of what they need.

But just how many is unclear because scientists and doctors disagree on what the "optimal" thresholds should be, according to Anne Looker, senior scientist at Centers for Disease Control and Prevention. So the percentage of American adults not getting enough vitamin D ranges from 32 percent to 74 percent, according to the analysis of the CDC's 2000 to 2004 nutrition examination surveys.

A shortage of vitamin D has been linked to several cancers, bone loss and unexplained muscle pain. Vitamin D also boosts our immune system and is needed for strong bones.

Dr. Vin Tangpricha, an Emory University endocrinologist who has been studying vitamin D deficiency for 10 years recommends about 10 minutes of sun every day —- without sunscreen. Then, apply sunscreen and enjoy the outdoors some more, he says.

Still, for people who burn easily or have fair complexions, two minutes is likely more appropriate.

CLIP 'N' KEEP!

WHAT IS VITAMIN D?

A fat-soluble vitamin produced when ultraviolet rays strike the skin and trigger vitamin D synthesis. Vitamin D also is naturally present in a few foods, including tuna, eggs, fortified milk and cod liver oil. It is needed for strong bones and helps boost the immune system. It's also important for overall good health.

HOW MUCH VITAMIN D IS ENOUGH?

The National Academies of Sciences currently recommends 200 international units (IU) of vitamin D for children and adults up to age 50, and 400 to 600 IU for adults older than age 50. However, researchers now question whether these levels are adequate for optimal health. Most researchers agree that daily intake of 800 to 1,000 IU would benefit many people —- especially those at increased risk of vitamin D deficiency, including babies who are exclusively breast-fed, older adults, people with darker skin and people with limited sun exposure.

HOW DO YOU GET THE DAILY ALLOTMENT?

You would have to eat 10 bowls of fortified cereal to get your daily recommended allotment of vitamin D. Or four glasses of milk. Or 6 ounces of tuna. Or 16 egg yolks.

DON'T OVERDO IT

Although vitamin D can be toxic when taken in too large a dose from supplements, natural exposure of the sun —- or filling up on vitamin D-rich foods like salmon or tuna —- doesn't cause the same harm.

WHAT SPF NUMBER IS RIGHT FOR YOUR SKIN?

The lighter your skin is, the higher your SPF should be. Light-to medium-skinned people should use at least a 30, but preferably 45, especially during great exposure to the sun between the peak hours of 10 a.m. to 2 p.m. Darker-skinned people should use at least SPF 15. An SPF of 15 filters at least 93 percent of the UVB Rays; 30 SPF filters 96 percent of the UVB rays; and 45 SPF filters 97 percent of the UVB rays.

UVA VS. UVB RAYS

They are both rays emitted by the sun, which can result in premature aging and skin cancer. UVA penetrates the ozone more easily, and can penetrate deeper into the dermis (second layer of skin). UVB is more responsible for the sunburn reaction but can also cause premature aging and skin cancer.

Sources: Dr. Craig Austin, a New York dermatologist, National Institutes of Health, CDC, Mayo clinic, columnist Chris Rosenbloom