In recent years, the news reports about vitamin D have been positively glowing — not unlike the golden rays that trigger natural production of the sunshine vitamin in the body. While it’s been well known for decades that vitamin D is critical for building healthy bones by helping to regulate calcium, more recent studies have linked getting more vitamin D to an impressive array of benefits including a lowered risk of cancer, diabetes, heart disease, hypertension, depression, infection — and maybe even better sexual health for men. Celebrity doctors and health gurus have recommended taking D supplements, some saying that vast numbers of Americans are deficient.

Not surprisingly, vitamin D sales skyrocketed in the U.S. from just over $30 million in August 2008 to almost $125 million by August 2010, according to the Nutrition Business Journal. Thousands of people have asked their doctors to check their blood vitamin D levels for the first time. Others may have applied sunscreen a little less vigilantly, in heeding the frequently-mentioned advice to let their skin soak up a few more solar rays each day to increase their vitamin D stores.

All of this fueled controversy. Many physicians are uncomfortable with the recent fervor surrounding D supplementation, and warn that people may be overdosing and harming themselves. A high intake of D supplements can promote toxic side effects such as heart and kidney damage, they counter. One preliminary study even suggests that high levels of vitamin D may increase men’s risk of aggressive prostate cancer. And many dermatologists argue that any benefits seen from getting more vitamin D through unprotected sun exposure is not worth an increased risk of skin cancer.

This debate leaves two questions: How much vitamin D do you really need — and how should you get it?

What to know

The minimum blood level for vitamin D has long been 20 nanograms per milliliter (ng/ml). “That’s what you need for skeletal health,” says Clifford Rosen, MD, director of the Center for Clinical and Translational Research at Maine Medical Center Research Institute. Around 2007, some experts began advocating a higher standard of 30 ng/ml along with a boost in the daily recommended intake, based on preliminary studies pointing to vitamin D’s protective effects. One study even linked low D levels with increased risk of premature death.

But skeptics warn that excitement about D’s benefits comes largely from studies of animals, lab dishes and population statistics — a far cry from large trials in real people that can show cause and effect.

“There’s no question the research is intriguing,” says Rosen. “The question is whether supplementing beyond what’s normally in the body has any impact.”

In 2010, Rosen joined a panel of colleagues formed by the Institute of Medicine, a not-for-profit, non-governmental organization affiliated with the National Academy of Sciences. The committee pored over more than a thousand studies to determine what the hard data on vitamin D actually reveal.

The result: The committee’s study review found that the majority of Americans have a blood vitamin D level of 20 to 30 ng/ml, and the data indicate that this level is sufficient for bone health. There was no strong evidence that increasing your blood level of vitamin D to 30 ng/ml by taking supplements offers any health benefits.

Furthermore, the committee found that most American adults can get the necessary level of vitamin D by taking in 600 IU a day (though people over age 70 may need 800 IU). That’s more than the daily intake of 200 to 400 IU previously recommended for most adults — but far less than the 1,000 IU that many prominent vitamin D enthusiasts advocate taking each day.

“There just isn’t enough reliable data to conclude that taking in higher amounts of vitamin D prevents health problems,” Rosen says.

Of course, the findings of the Institute of Medicine committee hardly represent the final word. The debate continues. Scores of physicians still believe that millions of Americans are indeed deficient in vitamin D, and they predict that future research on large human populations will show that taking D supplements offers benefits. For example, a trial of 20,000 men and women is now under way to see if taking vitamin D supplements lowers the risk of cancer, heart disease and stroke. We’ll be hearing more about vitamin D.

What to do

While physicians and researchers still have greatly conflicting opinions on vitamin D, there seems to be tacit agreement on a few points of action:

1. Eat more D-rich foods. While relatively few foods contain vitamin D, ensuring that you add the richest sources to your diet is smart. A three-ounce serving of salmon or mackerel provides close to the daily requirement or better. Breakfast cereal and milk are both D-fortified: One bowl provides about one quarter of your daily need. Other foods with respectable amounts of the vitamin include tuna, yogurt and eggs.

2. Don’t try to get more vitamin D from the sun. It’ll happen naturally. Even if you wear sunscreen faithfully and avoid unprotected sun exposure, as most experts recommend, you’re still catching some rays. This may explain why the Institute of Medicine scientists found, to their surprise, that most people have blood levels of vitamin D above the healthy 20 ng/ml level, even though vitamin D in the diet tends to fall below recommended levels. “The 15 to 20 minutes a day of unprotected sun exposure that most Americans get without thinking about it appears to be enough on average to generate meaningful amounts of vitamin D,” says Rosen.

Other physicians believe that purposely getting small amounts of unprotected sun exposure is a practical way to get more vitamin D. “We had a big debate in our meetings, and it was a difficult discussion,” says Rosen.

“[It’s] a poor recommendation,” adds James Spencer, MD, a dermatologist in St. Petersburg, Florida, and spokesperson for the American Academy of Dermatology. “Counseling sun exposure is impractical and doomed to failure because, while the cancer risks are proven, the benefits are not.”

3. If you take a supplement, go easy. Taking a common multivitamin that contains 400 to 800 IU of vitamin D can be the simplest way to ensure you get all the vitamin D that current guidelines say you really need (and those guidelines could change next month or year, of course). If you do decide to take a separate vitamin D supplement, don’t exceed 1,000 IU a day. “My vitamin D levels were 17 ng/ml, so I started taking 1,000 IU a day and they went to 53 in six months,” Spencer says. While taking 1,000 IU of supplemental D per day is safe, according to the Institute of Medicine, megadoses can bring higher risks. It’s easy to find vitamin D supplements packing 2,000 to 5,000 IU per pill, so be careful.

1. “Dietary Reference Intakes for Calcium and Vitamin D,” Institute of Medicine, report brief, November 2010, http://www.iom.edu/~/media/Files/Report%20Files/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D/Vitamin%20D%20and%20Calcium%202010%20Report%20Brief.pdf

2. “Vitamin D,” fact sheet, Office of Dietary Supplements, National Institutes of Health, November 2010, http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

3. “Position Statement on Vitamin D,” American Academy of Dermatology, June 19, 2009, http://www.aad.org/forms/policies/Uploads/PS/AAD_PS_Vitamin_D.pdf

4. “Independent Association of Low Serum 2-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D Levels with All-Cause and Cardiovascular Mortality,” Archives of Internal Medicine, June 23, 2008, http://archinte.ama-assn.org/cgi/content/abstract/168/12/1340

5. “Serum Vitamin D Concentration and Prostate Cancer Risk: A Nested Case-Control Study,” Journal of the National Cancer Institute, June 4, 2008, http://www.ncbi.nlm.nih.gov/pubmed/18505967

6. “How Vitamin D Can Benefit Men’s Health,” Medical News Today, May 31, 2005, http://www.medicalnewstoday.com/articles/25372.php

7. “The Vitamin D and Omega-3 Trial (VITAL), http://www.vitalstudy.org/