Vitamin D & Vitamin D Deficiency
What is vitamin D and why is it needed?
Vitamin D is one of the many nutrients our bodies need to stay healthy. Among the vitamin’s main functions, it helps the body:
- Absorb calcium. Vitamin D, along with calcium, helps build bones and keep bones strong and healthy.
- Block the release of parathyroid hormone. This hormone reabsorbs bone tissue, which makes bones thin and brittle.
Vitamin D may also play a role in muscle function and the immune system. The immune system is your body’s defense system. It helps protect it against infections and other illnesses. Taking vitamin D every day has been shown to reduce the risk of falling in older individuals.
Other ways vitamin D is thought to help us, and how much we would need to take, is an area of active research (and controversy). There have been studies to suggest that it might help prevent colon, prostate, and breast cancers. There is also some research that it might help prevent and treat diabetes, heart disease, high blood pressure, and multiple sclerosis. However, the results of many of these studies are either preliminary or under debate. Without other long-term research, even many of the researchers who conducted these initial studies are cautious about recommending vitamin D for the prevention of these diseases.
What are the sources of vitamin D?
You can get vitamin D through sun exposure, your diet, and supplements.
Vitamin D is produced when your skin is exposed to sunshine. The amount of vitamin D that your skin makes depends on such factors as the season (i.e., there’s usually less sunshine in winter months), the time of day (the sun’s rays are most powerful between 10 am and 3 pm), the amount of cloud cover and air pollution, and where you live (cities near the equator have higher UV levels). It’s the UV (ultraviolet) light in sunlight that causes your skin to make vitamin D.
Food sources (diet)
The best way to get enough vitamin D every day is to eat a variety of healthy foods from all food groups. The vitamin content of various foods is shown in the table.
Vitamin D Content of Various Foods
International Units per serving
- Cod liver oil, 1 tablespoon: 1360
- Swordfish, cooked, 3 ounces: 566
- Salmon (sockeye) cooked, 3 ounces: 477
- Tuna, canned in water, drained, 3 ounces: 154
- Orange juice fortified with vitamin D, 1 cup: 137
- Milk, vitamin fortified, 1 cup: 115-124
- Yogurt, fortified with 20% of the daily value of vitamin D, 6 ounces: 80
- Margarine, fortified, 1 tablespoon: 60
- Sardines, canned in oil, drained, 2 sardines: 46
- Liver, beef, cooked, 3 ounces: 42
- Egg yolk, 1 large: 41
- Cereal, fortified with 10% of the daily value of vitamin D, 1 cup: 40
- Cheese, Swiss, 1 ounce: 6
Source: Vitamin D. Health Professionals. Dietary Supplement Fact Sheet. National Institutes of Health. Office of Dietary Supplements. June 24, 2011
It is important to check product labels, as the amount of added vitamin D varies when it is artificially added to products such as orange juice, yogurt, and margarine.