Vitamin D – Benefits, Requirements and More

Vitamin D is an essential nutrient that promises great health benefits yet most adults fall short.

By Kathleen M. Zelman, MPH, RD

The sunshine vitamin is a hot topic and yet somewhat cloudy. Studies suggest vitamin D may go beyond its well-established role in bone health and may help reduce the risk for other conditions. It is found in virtually every tissue and cell in the body.

However, most adults fall short of meeting requirements because it is not abundant in food and the sun is not a reliable source. Vitamin D has been identified as a “nutrient of concern” in the 2010 and 2015 Dietary Guidelines for Americans with roughly 40 percent of adults worldwide deficient in vitamin D.

Meeting Requirements

The best approach to meeting vitamin D requirements is through sensible sun exposure, dietary sources and supplements of D3. However, most people, regardless of their diet, have difficulty meeting vitamin D requirements from food alone because of the limited number of foods naturally rich in vitamin D. The best sources are fatty fish such as salmon, sardines, trout, mackerel and tuna, in addition to fish liver oils. Most dietary vitamin D comes from food fortified with vitamin D such as milk, juices and breakfast cereals.

Experts disagree over what constitutes vitamin D deficiency and the optimal intake. Vitamin D status from diet, supplements and the sun is assessed with a simple blood test. Depending on whom you ask, sufficient levels range between 20 to 50 ng/ml and 40 to 80 ng/ml, while recommended intakes for adults are as low as 600 IU per day and as high as 5,000 IU per day. The Institute of Medicine (IOM) recommends the lower ranges while the Vitamin D Council aims for the higher ranges.

In 2010, the IOM substantially increased the Recommended Dietary Allowance (RDA) for people between 1 and 70 years of age, including pregnant and lactating women, to 600 IU per day and 800 IU per day for anyone over 71 years.

In contrast, the Endocrine Society recommends 600 to 1000 IU per day for ages up to 18 and 1500 to 2000 IU per day for ages 19 to 70+ and the International Osteoporosis Foundation recommends 800 to 1000 IU for older people.

Yet, even at these higher levels, some experts suggest the current recommendations only provide a fraction of what is needed for good health. “An intake from food, supplements and sunshine amounting to 7000 IU/day would be necessary for most Americans to achieve adequacy” says vitamin D expert, Robert Heaney, MD.

Overweight or obese individuals need 2 to 3 times more because vitamin D gets diluted in body fat. Certain conditions such as bariatric surgery, fat malabsorption, reduced renal function and some medications may require additional vitamin D to compensate for impaired absorption.

Dietary Supplements

With public health messages to avoid sun exposure and a lack of vitamin D rich foods, the use of supplemental vitamin D may be necessary to fill in the nutrient gaps. Vitamin D3, the type found in most foods, is the preferred form.

Supplements can be taken daily, weekly or monthly, and many health care providers recommend starting with a higher dose, then reducing after a month or two and continuing with a maintenance dose. Multivitamins also may provide some vitamin D — typically 400 IU, but with a range between 200 IUs and 10,000 IUs.

The Sunshine Vitamin

Most people get at least some of their vitamin D through sunlight exposure, but usually not enough to rely on. There are many variables affecting vitamin D synthesis from the sun but “the most important are age, skin color, skin exposure and sunscreen being the most important” says Heaney. “As the body ages, there is a decreased ability to synthesize vitamin D from exposure to the sun — most 70 year olds only synthesize 25 percent compared to a 20 year old.”

The IOM discourages people from exposure to sunlight due to increased risk of skin cancer. The American Academy of Dermatology’s 2009 Position states “there is no scientifically validated, safe threshold level of UV exposure from the sun that allows for maximal vitamin D synthesis without increasing skin cancer risk.”

How Much Is Too Much?

Safety concerns abound with high levels of fat soluble vitamins because of the potential for toxicity; however, vitamin D appears to be the exception.

Vitamin D toxicity is one of the rarest medical conditions and is typically due to extremely high doses. IOM set the tolerable upper limit at 4,000 IU per day whereas the Endocrine Society guidelines set the safe upper limit at 10,000 IU per day.

Vitamin D Research

Rickets in children and osteomalacia, osteopenia and osteoporosis in adults are the most well-established consequences of vitamin D deficiency. In addition, hundreds of studies during the past 15 years underscore interest in vitamin D’s potential role in helping to reduce the risk for other diseases such as some cancers, heart disease, diabetes and more. But for now, bone health is the most significant relationship with vitamin D.

Robert P. Heaney, M.D., professor of medicine and John A. Creighton University Professor Emeritus

Vitamin D Council:

U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans, 2005. 6th Edition, Washington, DC: U.S. Government Printing Office, January 2016

Hossein-nezhad, A. and Holick, M.F. Vitamin D for health: a global perspective. Mayo Clin Proc. 2013; 88: 720–755.

Holick, M.F. et al. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society Practice Guideline. J. Clin. Endocrinol. Metab. 2011, 96, 1911–1930.

Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D; The National Academic Press: Washington, DC, USA, 2011.