Vitamin D , Your Health and the Winter
By Andrea Anfuso-Sisto, RD
Vitamin D is a nutrient found in some foods that is needed for health and maintaining strong bones. It is required for your body to absorb calcium, which is the bones main building blocks, from foods and supplements. Vitamin D is also used by our muscles to move, our nerves to carry messages between the brain and every body part, and our immune systems need it to fight off invading bacteria and viruses. We usually associate Vitamin D with calcium and their protective effects from osteoporosis, but as you see, Vitamin D is found in cells throughout the body.
The body makes vitamin D when skin is directly exposed to the sun, but research shows that the winter months greatly reduce our supply of Vitamin D. Skin exposed to sunshine indoors through a window will not produce vitamin D. Cloudy days, shade, and having dark-colored skin also cut down on the amount of vitamin D the skin makes.
The following are the Recommended Daily Allowance for Vitamin D in International Units (IU):
|Birth to 12 months
|Children 1–13 years
|Teens 14–18 years
|Adults 19–70 years
|Adults 71 years and older
|Pregnant and breastfeeding
What foods provide vitamin D?
Very few foods naturally have vitamin D. Fortified foods provide most of the vitamin D in American diets.
- Fatty fish such as salmon, tuna, and mackerel are among the best sources.
- Beef liver, cheese, and egg yolks provide small amounts.
- Mushrooms provide some vitamin D. In some mushrooms that are newly available in stores, the vitamin D content is being boosted by exposing these mushrooms to ultraviolet light.
- Almost all of the U.S. milk supply is fortified with 400 IU of vitamin D per quart. But foods made from milk, like cheese and ice cream, are usually not fortified.
- Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and soy beverages; check the labels.
Vitamin D and supplements:
Vitamin D is found in supplements (and fortified foods) in two different forms: D2 (ergocalciferol) and D3 (cholecalciferol). Both increase vitamin D in the blood.
The safe upper limit for vitamin D is 1,000 to 1,500 IU/day for infants, 2,500 to 3,000 IU/day for children 1-8 years, and 4,000 IU/day for children 9 years and older, adults, and pregnant and lactating teens and women. Vitamin D toxicity almost always occurs from overuse of supplements. Excessive sun exposure doesn’t cause vitamin D poisoning because the body limits the amount of this vitamin it produces.
The best measure of one’s vitamin D status is blood levels of a form known as 25-hydroxyvitamin D. Levels are described in either nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL), where 1 nmol/L = 0.4 ng/mL.In general, levels below 30 nmol/L (12 ng/mL) are too low for bone or overall health, and levels above 125 nmol/L (50 ng/mL) are probably too high. Levels of 50 nmol/L or above (20 ng/mL or above) are sufficient for most people.
If your level is found on the ‘low’ side, you physician will likely prescribe a high dose Vitamin D supplement for several weeks to boost you to an optominal level. After that, it is important to continue to take a supplement daily, which may be recommended in the 2,000 – 4,000 IU range.
Vitamin D is being studied for its possible connections to several diseases and medical problems, including diabetes, hypertension, and autoimmune conditions such as multiple sclerosis. Two of them discussed below are bone disorders and some types of cancer.