Answers about Vitamin D
Q: I was recently diagnosed with vitamin D deficiency. How can I get more vitamin D, and are there any foods that I should be eating?
—Lyz from N.Y.
A: This is a great question because vitamin D deficiency has become more prevalent in recent years. Just last year, the National Center for Health Statistics published data showing that 33 percent of Americans were at risk of vitamin D deficiency or inadequacy based on serum blood levels. Vitamin D is sometimes referred to as the “sunshine vitamin” because our bodies make vitamin D naturally from sun exposure to the skin. Exposure to ultraviolet rays specifically triggers the conversion of cholesterol in the skin to vitamin D3, a form of vitamin D. We’ve all been taught to use sunscreen to prevent the harmful effects of exposure to UV rays, but all of this sunscreen use has led to another problem—vitamin D deficiency. Sunscreen blocks the absorption of UV rays; correctly applied sunscreen reduces our ability to absorb vitamin D by more than 90 percent.
Most of us recognize vitamin D as being important for bone growth, which it is. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. When you don’t get enough vitamin D, it puts you at risk for diseases such as rickets in children and osteomalacia in adults. That’s why the government started fortifying milk with vitamin D in the 1930s—rickets was a major health problem at the time. But vitamin D is not just important for healthy bones—it actually has several other important functions in the body, including maintaining a healthy immune system and modulating proper cell growth. Recent studies have linked vitamin D deficiency to cardiovascular disease, osteoporosis, autoimmune disease, and several types of cancer.
So how much vitamin D do we need? Currently there is a lot of scientific debate over what the optimal amount of vitamin D is. The official Recommended Dietary Allowance (RDA) in adults is 600 International Units (IU) per day and 800 IU for those over age 70. But many groups including Harvard’s School of Public Health are recommending much larger amounts based on the most current research.
What are the best ways to get an adequate amount of vitamin D? The best way is through exposure to sunlight. Just 10 to 15 minutes of sunlight exposure can provide 3,000 to 20,000 IU! The problem is that the amount of vitamin D that we get from sun exposure varies considerably, depending on several factors, including geographic latitude and skin color. Sunlight is generally weaker in northern latitudes, leading to less vitamin D synthesis. Also, people with darker skin tones generally need a lot more sun exposure to synthesize vitamin D because melanin reduces the skin’s ability to produce vitamin D from sunlight. Of course, it is also important to protect your skin from the harmful effects of sun exposure, which leads to millions of cases of skin cancer every year in the U.S.
To further complicate the issue, there are relatively few natural food sources of vitamin D. The best sources are fatty fish such as salmon, tuna, sardines, and mackerel. Canned fish generally has more vitamin D than fresh. Small amounts of vitamin D are also found in egg yolks, beef liver, and some cheeses. In fact, a new analysis done by the USDA found that eggs contain 64 percent more vitamin D than the last time they were analyzed by the government in 2002. This increase is probably due to changes in the diet of chickens by egg producers. In addition to natural food sources, many cereals, milk, and dairy products are also fortified with vitamin D. The U.S. also mandates the fortification of infant formula with vitamin D. Mushrooms also can be a source, especially if treated with UV rays during growth. Here are some specific levels taken from the N.Y. State DOH website:
Herring: 1,383 IU per 3 ounces
Salmon, canned: 530 IU per 3 ounces
Cod liver oil: 450 IU per teaspoon
Mackerel: 306 IU per 3 ounces
Oysters: 272 IU per 3 ounces
Shiitake mushrooms, dried: 249 IU per 4
Sardines, Atlantic, canned in oil: 203 IU per ½ cup
Tuna, canned in oil: 200 IU per 3 ounces
Large egg: 41 IU (new data)
Tofu: 120 IU per 1/5 block
Cow’s milk: 100 IU per 8 ounces
Soymilk: 100 IU per 8 ounces
Orange juice: 100 IU per 8 ounces
Cereal: 40 IU per serving
If you are concerned that you are still not getting enough vitamin D through sun exposure and food sources, you can always take a vitamin supplement. Most multivitamins provide about 400 IU of vitamin D.
So what’s the take-home message with vitamin D? Vitamin D is very important for the body, and the more we learn about it, the more true this seems to be. If you’re concerned about vitamin D deficiency, consult your physician and get tested. Try to get brief periods of sun exposure daily, but after 5 to 15 minutes, make sure you apply sunscreen. To get the rest of your daily needs, incorporate natural food sources into your diet and, if needed, add a vitamin supplement.
Dr. Ruder is a mom of a two-month-old daughter, an emergency physician at Coral Springs Medical Center near Fort Lauderdale, FL, and a recipe developer and blogger at TheFoodiePhysician.com.
Want to read more blogs by Sonali Ruder, DO? Here’s her recent blog about the importance of eating breakfast.