Bravo to those who seek cover from the sun to prevent premature aging, melanoma and other skin damage. But it’s important to recognize that more sun protection means less Vitamin D, which our bodies produce after exposure to UVB rays.

Experts agree that Vitamin D is essential for good health and wellness. However, there is no consensus about how many diseases it can prevent, how much is necessary and how people should go about getting enough.

What is known is that many of us don’t get enough. A 2010 study in Nutrition Journal found that 42 percent of U.S. adults were deficient in Vitamin D, with the highest rates among African Americans and Hispanics.

Children are also at risk: A report in the Archives of Pediatric and Adolescent Medicine showed that 12 percent of children had Vitamin D deficiencies, and an additional 40 percent exhibited higher but still insufficient levels.

“Vitamin D, working with calcium, is very clearly critically important for bone health, particularly in youth during skeletal development up through puberty and . . . in your 50s, 60s and beyond, for the prevention of osteoporosis, fractures and falls,” said Steven Clinton, a professor of medical oncology at Ohio State University. Clinton recently served on an Institute of Medicine committee charged with reviewing Vitamin D intake recommendations.

Vitamin D deficiency is common and bad for bone health, but how to address it is a matter of debate. (Rosemary Calvert/GETTY IMAGES)

Additionally, in the last year alone, numerous published studies have concluded that Vitamin D might play a role in preventing everything from cancer and cardiovascular disease to Alzheimer’s, diabetes, depression, immune function and weight gain.

This research, however, has not convinced everyone.

“Yes, there are some observational studies suggesting that men and women who have higher blood levels of Vitamin D have a lower risk of cancer, heart disease, diabetes and other health problems, but . . . these results may be due to other, confounding factors,” said JoAnn Manson, chief of preventive medicine at Harvard-affiliated Brigham and Women’s Hospital, who served on the IOM committee.

She hopes to provide some answers as principal investigator of the first large-scale, randomized clinical study on the effect of moderate to high doses of Vitamin D on cancer, cardiovascular disease and a range of other conditions.

Different recommendations

For now, the IOM recommends 400 international units of dietary Vitamin D a day for babies up to a year, then 600 IU up to age 70, with 800 IU for those older than 70, in order to maintain a blood level of at least 20 nanograms per milliliter. That amount is considered optimal for bone health for most people.

Manson noted that this assumes minimal sun exposure and added that people with osteoporosis and those who are obese or who have malabsorption or other medical problems might require more, and should consult with their doctors.

Clinton said that while he is convinced that Vitamin D could decrease susceptibility to cancer, “we really do not have the kind of information we need yet to tell someone what blood level of Vitamin D you should have at what stage of your life to clearly impact your risk of developing any of some 100 different kinds of cancer people get. We have an enormous amount left to learn, and need more research to help us sort this out.”

Still, those who fervently believe that Vitamin D has more wide-ranging health effects tend to advocate for more.

“It’s hard to know what the ideal blood level is, but our policy is that your Vitamin D level should be a natural one, similar to what a roofer or a lifeguard might have, and that’s . . . right around 50 [nanograms],” said John Cannell, president of the Vitamin D Council, a nonprofit advocacy group based in California. “That requires daily sun exposure or an intake of 5,000 IU a day,” which is above the IOM’s suggested upper limit of 4,000 IU, and far above its recommendations for maintaining optimal bone health.

The Endocrine Society’s advice falls somewhere in the middle. Its 2011 guidelines say people may take 1,500 to 2,000 IU of Vitamin D daily to consistently raise blood levels above the 30 nanograms that it deems sufficient.

So even if your crystal ball could clarify which recommendations to follow, how would you get that amount on your dinner plate?

Vitamin D is naturally present in a small number of foods such as fatty fish, eggs and cod liver oil, and it is added to others, including milk. But “it’s not easy to get all that you need through diet alone,” said medical researcher Lily Li, who works on a Vitamin D test development team at Ortho-Clinical Diagnostics, based in in Raritan, N.J.

For example, she points out that eight ounces of fortified milk has about 100 IU of Vitamin D — enough to prevent the skeletal disorder rickets in small children but far short of even the most conservative recommended intake.

Sunbathing and Vitamin D

A word of caution to those considering tossing their SPF 50 and hitting the pool after work for some sun: While the natural skin production of Vitamin D is rapid and robust, it can also be difficult — not to mention incredibly inconvenient — to get enough UVB rays to meet all of your Vitamin D needs, especially year-round.

“If you go out in a bathing suit with no sunblock in the middle of the day and the sun is high enough in the sky, within minutes you’ll have made 1,000 IU, but we are not just talking about exposing your hands,” Cannell said. “It takes true sunbathing for 15 or 20 minutes a day with a majority of skin surface exposed to the sun — meaning that you can’t have clothes covering the major parts of your body — which just isn’t practical for most people.”

He adds that early-morning, late-afternoon and winter rays won’t cut it in Washington or many other parts of the country, because the sun is too low in the sky for your skin to synthesize any of the vitamin.

Curious whether you’re making or eating enough Vitamin D? A doctor probably won’t be able to tell just by looking at you, and the symptoms of an insufficiency or deficiency can be nonspecific, such as fatigue and lack of muscle strength, Li said.

The classic diseases caused by Vitamin D deficiency — rickets and osteomalacia in adults — are now relatively rare, she added. It’s also worth noting that most experts do not recommend testing, because of variation in laboratory results, seasonal fluctuations in Vitamin D blood levels and the lack of consensus as to what constitutes an optimal, a normal or a worrisome level of Vitamin D.

Instead, all four experts I spoke with say that supplements are probably the answer for most of us. Both the IOM and the American Academy of Pediatrics recommend this, beginning with breast-fed newborns, who should be given 400 IU of liquid Vitamin D until they are weaned onto formula or cow’s milk.

However, like pretty much everything else related to this topic, there is no real agreement on supplementation.

For example, the U.S. Preventive Services Task Force came out against low-dose Vitamin D and calcium supplements for healthy older women in June, saying that an extra 400 international units do not prevent bone fractures and that it’s better to get Vitamin D from diet and the sun. At the same time, the task force acknowledged that there is inadequate evidence regarding higher amounts of the supplement and its effect on other aspects of health.

To complicate matters further, this report came a month after the task force recommended that all adults 65 and older take Vitamin D to help prevent falls.

In light of all the controversy and the absence of consensus, many doctors preach moderation.

“If you are otherwise healthy and eating a diverse diet that contains [Vitamin D-rich] foods, you should not have to supplement,” says Clinton. “However, as a clinician and a cancer doctor, I know that many people feel more comfortable with taking a supplement each day, like a multivitamin that has [the recommended amount of] Vitamin D 2 . The levels in there are certainly safe, and I’m very comfortable with folks that want that added insurance.”