Are You Getting Enough Vitamin D?

Are You Getting Enough Vitamin D?

Julian Whitaker, MD

Unlike vitamins A, B, C, E, and K, which you get from your diet, vitamin D is synthesized when your skin is exposed to ultraviolet-B (UVB) radiation from the sun. This fat-soluble vitamin is then transported to the liver and kidneys, where it is converted into the biologically active forms required by tissues throughout your body.

Vitamin D performs a host of crucial roles. It is necessary for calcium absorption and utilization. It regulates the activity of dozens of genes and promotes normal cell division and growth. It is also intimately involved in immune function, insulin secretion, blood clotting, and blood pressure control.

The amount of vitamin D you produce is directly related to your UVB exposure, and for most North Americans, this equates to reduced levels in the wintertime. If you live in one of the southern states and you get outside in direct sunlight several times a week, you probably have decent levels of vitamin D. However, at latitudes 40 degrees or more north or south of the equator (Reno, Denver, Indianapolis, and Philadelphia all lie near this parallel), the angle of the sun during winter allows no UVB radiation to hit the earth. You could stand outside buck naked in Seattle or Chicago at this time of year and you still wouldn’t produce any vitamin D!

Now you can see why deficiencies of this multifaceted vitamin are so common—and why you need to boost your levels by taking supplemental vitamin D.

The Cancer Connection

More than a dozen forms of cancer have been associated with vitamin D deficiencies. That’s because this vitamin inhibits cell proliferation, the out-of-control growth that marks cancer; stimulates differentiation, which keeps cells on the normal growth track; and suppresses the growth of new blood vessels that nourish tumors.

In a meta-analysis published in the February 2006 issue of the American Journal of Public Health, researchers looked at 63 studies of vitamin D status and cancer risk and found that the majority of them demonstrated a protective role of adequate vitamin D levels.

This analysis also confirmed that people living in the less sunny northeastern states and those with darker skin are more likely to have vitamin D deficiencies, and that because of this deficiency, African-Americans are at increased risk of death from breast, prostate, colon, and ovarian cancers.

How significant is the impact of vitamin D deficiency? In a 2005 paper, leading vitamin D researchers estimated that it is responsible for 50,000–63,000 premature cancer deaths in this country every year. They also pegged the annual economic burden of vitamin D deficiencies at $40–$50 billion!

Deliverance From Heart Disease?

It has been observed for decades that, in addition to wintertime increases in deaths from heart attack and other cardiovascular diseases, mortality rates are higher in colder, northern areas. Hypertension and heart disease are also more common in African-Americans who, because of their dark skin, have lower levels of vitamin D. (Individuals with dark skin are at risk because they require at least 10 times more sun exposure to produce the same amount of vitamin D as those with fairer complexions.)

There are lots of reasons to link vitamin D deficiencies with heart disease. This vitamin helps maintain normal calcium levels and control smooth muscle proliferation in the artery walls. It has been shown to reduce levels of C-reactive protein, a marker of inflammation linked to heart attack risk. There is also an inverse relationship between vitamin D levels and blood pressure—raising vitamin D levels with high-dose supplementation or exposure to UVB radiation reduces blood pressure in study subjects.

I’ll be the first to admit that there are no definitive studies on vitamin D as a treatment for cardiovascular disease. That’s because there’s no money to be made on this inexpensive, over-the-counter vitamin, although a number of drug companies are sponsoring research on synthetic, patentable versions. Nevertheless, ensuring optimal vitamin D levels should be a consideration for everyone with hypertension, heart failure, or any other disorder of the cardiovascular system.

Low Levels Linked to Fractures

Vitamin D is best known for its effects on the bones. In addition to facilitating calcium absorption and making bones stronger, it also enhances muscle function and improves balance and agility, which reduces risk of falls and fractures.

Deficiencies in this vitamin are extremely common among people with hip fractures. In a 2005 study conducted at King’s College Hospital in London, medical records of 103 patients hospitalized with hip fractures were reviewed, and “almost universal vitamin D inadequacy” was noted—especially among those admitted during the winter (98 percent were deficient versus less than 83 percent in the summer). Similarly, Australian researchers recently found that older people in assisted living facilities or nursing homes could dramatically reduce their risk of falls simply by taking vitamin D supplements.

Another very common but largely overlooked vitamin D-deficiency-related bone disease is osteomalacia. Marked by chronic diffuse pain and tenderness at specific points, it is often misdiagnosed as fibromyalgia. If applying moderate pressure on your sternum (breastbone) hurts, you should have your vitamin D level checked to rule out osteomalacia. The good news? It is easily corrected with supplemental vitamin D.

How to Reverse D Deficiencies

I hope this information encourages you to look into your vitamin D status. This is especially important during the winter if you live in a northern state. But keep in mind that factors other than seasons, geography, and skin tone also contribute to vitamin D deficiencies. Up to 80 percent of nursing home residents are deficient, as are more than half of all hospitalized patients. Obese people are prone to deficiencies (their excess fat stores make vitamin D less bioavailable), as are patients with kidney, liver, and some bowel diseases, who cannot absorb or convert vitamin D properly.

Another at-risk group is sun phobics who never leave the house unless they’re slathered in sunscreen. I appreciate the adverse effects of UV radiation, including the increased risk of skin cancer, but even an SPF of 8 blocks vitamin D production by 95 percent! I’m not saying you should throw your sunscreen away altogether, but I do recommend that you make a concerted effort to get about 15 minutes of unprotected sun exposure several times a week. If you are dark-skinned or live at a higher latitude, you’ll require more time in the sun for optimal vitamin D production.

You can also get some vitamin D in your diet. It is most abundant in salmon and other cold-water fish, which explains why Eskimos and others who live in the far North are protected against deficiencies. (Cod liver oil, which many of you endured during the winters of your childhood, is another excellent source of vitamin D.)

But aside from fish, dietary sources of vitamin D are few and far between. Although many foods used to be enriched with vitamin D, today only a handful of foods are fortified. The main one is milk, but you’d have to drink four to six glasses just to get the RDA of 400 to 600 IU!

That leaves vitamin D supplements, which every physician should recommend.


  • To ascertain your vitamin D level, ask your doctor for a 25(OH)D blood test, the only accurate test of vitamin D status. Optimal levels are between 50 and 70 ng/mL.
  • In my clinical experience, most adults need a minimum of 2,000 IU of vitamin D per day to achieve these levels.
  • Fears of toxicity are overblown. Vitamin D is perfectly safe at these levels and, for short periods of time, in much larger doses. Very high-dose vitamin D may be required to overcome deficiencies and should be taken under the care of a physician.


  • Flicker L et al. Should older people in residential care receive vitamin D to prevent falls? Results of a randomized trial. J Am Geriatr Soc. 2005 Nov;53(11):1881-1888.
  • Garland CF et al. The role of vitamin D in cancer prevention. Am J Public Health. 2005 Dec 27; .
  • Grant WB et al. Comparisons of estimated economic burdens due to insufficient solar ultraviolet irradiance and vitamin D and excess solar UV irradiance for the United States. Photochem Photobiol. 2005 Nov-Dec;81(6):1276-1286.
  • Moniz C et al. Prevalence of vitamin D inadequacy in osteoporotic hip fracture patients in London. Curr Med Res Opin. 2005 Dec;21(12):1891-1894.

Modified from Health & Healing with permission from Healthy Directions, LLC. Photocopying, reproduction, or quotation strictly prohibited without written permission from the publisher. To subscribe to Health & Healingclick here.

Print Friendly, PDF & Email