Quinn on Nutrition: Getting enough Vitamin D but not too much

June 1, 2015

Vitamin D seems to be the darling nutrient these days. And probably for good reason. This nutrient is critical for the growth and maintenance of sturdy bones. Without it, calcium — the body’s primary mineral — cannot be absorbed. Yet vitamin D does more than that, according to the National Institutes of Health (NIH) Office of Dietary Supplements. It regulates how our nerves and muscles work; and it reduces internal inflammation that we now know can lead to chronic diseases like heart disease and type 2 diabetes.

Historically, before we began to fortify milk with vitamin D and open vitamin shops, our most abundant source of vitamin D was the sun. Ultraviolet (UV) rays that strike bare skin trigger the formation of the active form of this essential nutrient.

Today, when many of us are not sunbathing on the beach for various reasons, we look to food and supplements for this important nutrient. Very few foods contain Vitamin D naturally, however. Best sources are dark-fleshed fish like salmon or tuna since vitamin D resides in the oils of these fish. Beef liver, cheese, egg yolks and mushrooms contain some vitamin D as well. One product, Monterey Mushrooms, contains a day’s supply of vitamin D in each serving. Fortified foods, such as milk, some juices and cereals (such as Total®) also contribute vitamin D.

How do we know if we are getting enough? One good indicator, says the NIH, is a blood test that measures 25-hydroxy-vitamin D, or 25(OH)D. If this is low, medical professionals often prescribe vitamin D supplements. A recent study on men and women in the Journal of the Academy of Nutrition and Dietetics reported that people over the age of 50 absorbed more vitamin D from a supplement when they took it under these conditions:

Take it after a meal. Vitamin D is absorbed better with food than on an empty stomach, say researchers.

Take it after a meal that contains fat. Remember vitamin D is a fat-soluble vitamin which means it likes to be involved with fat. But it doesn’t have to be a super bacon cheeseburger with fries. Eating a meal with just a moderate amount of fat — such as oil, peanut butter, low fat milk or yogurt, fish, chicken, or salad dressing — increased the amount of vitamin D absorbed from a supplement by at least a third, according to this study.  

We can’t get too much vitamin D from sun exposure, say scientists, since the body carefully regulates this. But we can get toxic doses from supplements. More than 4000 International Units (IU) a day may be unsafe over the long term for anyone over the age of 9 years, says the NIH.





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