Vitamin D deficiency in America:
Who's at risk? Why is is a concern?

map of US showing areas of weak sunshine
If you live in the colored areas of this map, you probably do not get enough winter sun for your body to produce adequate Vitamin D. (North of 35° latitude.)

By Daniela Radulescu, M.D., member of Medical Advisory Board for TriVita, makers of Essential D vitamin D supplement.

In recent years, many researchers and the media have touted the health benefits of Vitamin D. It's been shown to be especially beneficial in protecting against colds and the flu, maintaining bone and muscle and reducing the risk of certain cancers. But we've also heard that a majority of people are deficient in this powerhouse vitamin, which suggests that supplementation may be necessary. The problem is that recommendations for intake have varied over the years, creating confusion for those who seek the maximum health benefits.

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An epidemic: Vitamin D deficiency

According to experts, anywhere from two thirds to 95% of Americans are lacking Vitamin D. Globally, it's estimated that as much as 50% of the world's population is at risk for deficiency. That's especially alarming considering that Vitamin D deficiency has been associated with an increased risk of many serious diseases, including cancer, osteoporosis, Alzheimer's disease and diabetes.

So what causes Vitamin D deficiency? It's primarily a lack of sunlight. You see, Vitamin D is produced in the skin by UVB light, and with our increasingly indoor culture, people aren't getting enough sun exposure. And when they do head outside, they tend to cover themselves with sunscreen, which can block Vitamin D production. (SPF 8 sunscreen reduces production of vitamin D by 95%!)

In winter, it becomes even more difficult to get the sunshine required, especially for those who live at high latitudes. In fact, those who live north of 35 degrees latitude (around Atlanta, GA) are likely to produce little -- if any -- Vitamin D during winter. In times past, people could build up reserves of Vitamin D through summertime sun exposure. But again, the move toward indoor pursuits has made this buildup less and less likely.

Groups most at risk for Vitamin D deficiency include infants fed exclusively breast milk, people with dark skin-color, the elderly, and those with diseases such as cystic fibrosis, cholestatic live, inflammatory bowel disease, or obesity.

So, how much Vitamin D is enough?

If so many people are deficient, the next question becomes, how much Vitamin D should they get each day? In summer sun, a person in a swimming suit (without sunscreen) can make approximately 10,000 international units (IU) of Vitamin D in just 15 minutes. In the late 1990s, that figure led researchers to speculate that 10,000 IU of Vitamin D daily appeared to be safe. However, most official recommendations fall well below that number.

In 2010, the independent, nonprofit Institute of Medicine (IOM) released guidelines that recommended adults get 600 IU of Vitamin D to maintain healthy bones, with an upper limit of 4,000 IU. This caused an uproar in the medical community, as research had shown much more Vitamin D was required to reduce the risk of the serious conditions linked to Vitamin D deficiency. Plus, research had shown that toxicity only occurred at 40,000 or more IU per day.

In 2011, the Endocrine Society, a body of international hormone specialists, published guidelines recommending 1,500-2,000 IU for adults, with an upper limit of 10,000 IU, to prevent and treat Vitamin D deficiency.

The nonprofit Vitamin D Council contends that for proper functioning, a healthy adult body uses approximately 3,000-5,000 IU per day. Thus, it recommends at least 5,000 IU of supplemental Vitamin D3 per day for adults, in absence of proper sun exposure. Vitamin D3 is the kind naturally produced by the body.

So again, we ask the question: how much is enough? The answer: it depends. Individual needs for Vitamin D vary based on current levels, age, weight, overall health, amount of sun exposure and even genetics. To determine how much Vitamin D you need, ask your health care provider for a Vitamin D blood test. You will need to have your Vitamin D levels tested and then monitored periodically to ensure you're getting the right amount.

Remember, an adequate supply of Vitamin D has been proven to help protect against colds and the flu, maintain bones and muscles and even help reduce the risk of certain cancers.

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Join the conversations:
Showing comment(s)
May 10, 2016

In your reply to Wendy's comment, you mentioned that the NY Dept of Health says we used to be able store enough Vitamin D during the spring, summer and fall to last us through the winter. Why is that no longer the case? Is it because most of us use sunscreen?

Mike, contributing writer for
May 12, 2016

Hi Kas,

Thank you for your question. This Vitamin D info sheet from Creighton University School of Medicine suggests that, today, very few of us spend enough time outdoors that we're able store up a 3 or 4 month supply of vitamin D to carry us through the winter months. So, lifestyle changes is probably the big difference... though you are correct that wearing sunscreen reduces the amount of vitamin D we produce from sun exposure.

But on that same topic, the author of this Washington Post article on Vitamin D asked (and then answered) a very interesting question; how is it that people were able to live in northern regions for thousands of years without suffering vitamin D deficiency if 1) it is nearly impossible to produce adequate vitamin D just from sun exposure during the winter and 2) supplements weren't around? Her answer: cultures in those areas traditionally ate a lot of fatty fish which is one of the best dietary sources of vitamin D.

June 14, 2012

I came across your article when I was searching to see how much natural sunlight is recommended each day in order to get enough Vitamin D. I see you mention 15 minutes on a summer day as being more than adequate. If you are interested, I found more specific instructions at

The National Institutes of Health says that it is very hard to say just how much sun exposure a person needs because there are so many significant variables to consider -- cloud cover, air pollution, sunscreen strength and amount, season, time of day and a person's age and skin color. They say that glass completely blocks the UV rays needed for our body to produce natural Vitamin D but I wonder if we get ANY vitamin D from indirect sun, like sitting outdoors in the shade?

One thing I found very interesting is that the body can store Vitamin D in our fat cells and release it as needed. Does any one know how long the body's stored reserves of Vitamin D can last?

Mike, contributing writer for
June 14, 2012

Hi Wendy,

The State of New York Department of Health website says that our body can store enough vitamin D during the spring, summer and fall to carry us through the winter months. Their recommendation is 5-15 minutes of sunshine, 2-3 times per week. During all other times of sun exposure, however, they recommend slathering on SPF 15 or higher sunscreen. It is not possible to overdose on vitamin D from the sun (though sun UV damage is the obvious concern), however, because the body stores vitamin D they recommend against consuming more than 2000 IU of vitamin D supplement without a prescription.

As for your question, we came across this interesting Australian study addressing your question, can we get adequate vitamin D from sitting in the shade? It suggests that, because UVB wavelengths scatter (and those are the type of UV rays that initiate vitamin D production in the body), we still get about 50% of the sun's direct UV rays when we are under the shade of a tree or umbrella. Sitting in the shade of a north-facing veranda, however, exposes us to only 11% of full sun strength and sitting in car with the windows up provides us with zero. So, they summarize that sitting in the shade may provide us with a reduced level of the UV rays needed for vitamin D production while not subjecting us to the higher UVA levels.

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