Muscles need vitamin D to move, and nerves need it to carry messages to the brain and the rest of the body. The immune system needs vitamin D to fight off bacteria and viruses. With calcium, vitamin D helps to protect older adults from osteoporosis.
Vitamin D is made by the body when skin is directly exposed to the sun. Most people meet at least some of their vitamin D needs this way.
› Health benefits
Vitamin D is being studied for its connection to several health issues. These include diabetes, hypertension and autoimmune conditions.
As people age, millions can develop or are at risk of osteoporosis. It is one consequence of not getting enough calcium and vitamin D over the long term. Supplements have been shown to reduce the risk of bone loss and fractures in elderly people.
Some studies have shown that vitamin D may protect against colon cancer and even prostate and breast cancers. However, higher levels of vitamin D have been linked to higher rates of pancreatic cancer. More research needs to be done in order to say whether vitamin D does help reduce the risk of cancers.
› How much do I need?
The amount needed daily is dependent on age. For women, it changes during pregnancy and when lactating. Ages 1 to 70: 600 IU daily; adults 71-plus: 800 IU per day. Pregnant and breastfeeding teens and women: 600 IU daily.
When vitamin D levels in the blood become too high, it can be harmful to the body. Signs of toxicity include nausea, vomiting, poor appetite, constipation, weakness and weight loss. When too much vitamin D raises calcium blood levels, it can cause confusion, disorientation and problems with heart rhythm. Excessive levels of vitamin D can also damage the kidneys.
Vitamin D may interact with other supplements or medications. Prednisone and other corticosteroid medicines used to reduce inflammation impair how the body handles vitamin D, leading to lower calcium absorption and loss of bone over time.
The weight-loss drug orlistat (Xenical and Alli) and the cholesterol-lowering drug cholestyramine (Questran, LoCholest and Prevalite) can reduce the absorption of vitamin D.
Phenobarbital and phenytoin, which are used to prevent and control epileptic seizures, increase the breakdown of vitamin D and reduce calcium absorption.
› In foods
Very few foods naturally contain 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, egg yolks and mushrooms provide small amounts. Some mushrooms can be exposed to ultraviolet light, which boosts their vitamin D content.
Almost the entire milk supply in the U.S. is fortified, with 400 IU of vitamin D per quart. However, foods made from milk 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 labels to see if it has been added.
› Dietary supplements
Vitamin D can be found in supplements in two forms: D2 (ergocalciferol) and D3 (cholecalciferol).
Because vitamin D can come from food, sun and supplements, the best measure of one’s vitamin D is through blood levels. Some Americans are vitamin D deficient, and almost no one has levels that are too high. Young people in general have higher levels than older people, and males have higher levels than females.
Certain groups in particular may not get enough vitamin D:
- Breastfed infants because human milk is a poor source of the nutrient.
- Older adults because their skin doesn’t make vitamin D when exposed to sunlight as efficiently as when they were young, and kidneys are less able to convert vitamin D.
- People with dark skin, because their skin has less ability to produce vitamin D from the sun.
- People with disorders such as Crohn’s or celiac disease who don’t handle fat properly, because vitamin D needs fat to be absorbed.
- Obese people, because their body fat binds to some vitamin D and prevents it from getting into the blood.
Please consult your health care provider before making changes to your vitamin/supplement regimen.