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Vitamin D allows your body to absorb calcium. Without it, your bones can become brittle and weak. In adults, too little vitamin D can lead to malformed bones and osteoporosis. In children, vitamin D deficiency once caused many cases of rickets, a bone disease and a major public health problem in the U.S. Fortifying the milk supply with vitamin D virtually eliminated the disorder.
Vitamin D for Heart and Mind
Low blood levels of vitamin D may have effects beyond your bones. Studies find a greater risk of heart problems and a greater risk of depression in older adults with low levels of vitamin D. And though it's not clear why, people taking a vitamin D supplement were 7% less likely to die than those who didn't take a daily supplement in one study. In children, researchers have found more severe asthma when vitamin D levels are low.
Vitamin D Comes From Skin
In a perfect world, you'd never have to worry about getting enough vitamin D. Your body produces it on its own. The trick is exposing some portion of your skin to direct sunlight for 15 to 30 minutes a few days a week. But the UV rays that stimulate production of vitamin D can also cause skin cancer. So most experts don't recommend getting your vitamin D from sun exposure.
Vitamin D Where You Live
The darker a person's skin, the more difficult it is to get vitamin D from sunlight. Fair-skinned people might be willing to risk the 10 to 15 minutes they need to get enough. But there's still a problem. Unless you live south of a line from Los Angeles to Columbia, S.C., there may not be enough sunlight year round to produce all the vitamin D you need. Some people may need other sources.
Who's at Risk for "D" Deficiency?
Studies find vitamin D deficiency can affect adults, infants, children, and adolescents. Your diet may increase your risk if it's low in milk or the foods that naturally contain vitamin D, such as salmon and eggs. Most people with low blood levels of vitamin D don't notice any symptoms. Others risk factors include:
- Obesity
- Digestive disorders like celiac disease
- Older age (50+)
- Some medications
The combination of high blood pressure and vitamin D deficiency could be deadly. In one observational study, people with hypertension and a vitamin D deficiency were twice as likely to have a cardiac event than other people in the study. The lack of vitamin D was not linked to cardiovascular problems in those without hypertension.
Vitamin D and Breast Cancer
Low vitamin D may worsen the prognosis for women with breast cancer. In one study, women deficient in vitamin D when they were diagnosed had a 94% greater chance of the cancer spreading. They also had a 73% greater chance of dying over the next 10 years. Other studies suggest that vitamin D may even offer protection against developing breast cancer.
Vitamin D and Other Cancers
Vitamin D may offer some protection against at least two other cancers: colon cancer and prostate cancer. But vitamin D isn't a magic bullet. The cancer-fighting benefit may be limited to people who are otherwise healthy, not overweight, and exercise.
Vitamin D and Depression
It isn't clear how they are related. But studies have linked low levels of vitamin D to depression among older men and women. One possible explanation is that lack of vitamin D causes the parathyroid gland to produce more hormone. Low levels of vitamin D and higher levels of parathyroid hormone have been linked to depression severity.
Vitamin D and Weight Gain
After menopause, most women gain weight until they reach their mid 60s. There is evidence, though, that taking a vitamin D and calcium supplement may slow that weight gain. In one study, women who were not getting enough of those two nutrients at the start were 11% less likely to gain weight and more likely to maintain their weight or even lose weight as a result of taking the supplement.
Vitamin D and Children
Evidence shows that children who get adequate vitamin D, either from the sun or from supplements, may have a reduced risk of developing type 1 diabetes. Studies also link inadequate vitamin D to more severe childhood asthma. Children with asthma who have low vitamin D levels have more hospitalizations and use more asthma medications.
Start Your Day With Vitamin D
One way to get vitamin D is through your diet. In the U.S., nearly all milk is fortified with vitamin D, and many brands of orange juice are, too. Even ready-to-eat breakfast cereals can contain a healthy dose. So just by making sure you eat breakfast, you can make every day a "D day."
Vitamin D at Dinner
Fish — especially fatty fish like salmon, tuna, mackerel, and sardines — are a good source of vitamin D. One 3-ounce portion of cooked salmon can provide nearly 200% of the recommended daily value of vitamin D. Three ounces of specially grown mushrooms that have been exposed to UVB light can provide 100%.
Eggs, Cheese, and Vitamin D
Other food sources of vitamin D include egg yolks, cod liver oil, beef liver, margarine, yogurt, and some cheeses. While milk has been fortified in the United States since the 1930s, the same is not true for all dairy products. Cheese and ice cream may be a tasty source of calcium, but you need to read the nutrition label to know whether or not you're getting vitamin D.
Vitamin D Supplements
Most Americans already have enough vitamin D in the bloodstream for good bone health. For those who want or need to boost their intake of vitamin D, supplements are an option. Most multivitamin tablets contain 400 IU of vitamin D. You can also find vitamin D by itself in higher-dose tablets and in combination with calcium.
D2 or D3? That's the Question.
Vitamin D is available in supplements in two forms: D2 and D3. Both forms are effective, and either can be taken to ensure adequate levels of vitamin D. But 2 is not equal to 3. D3 is the kind of vitamin D the body makes, and recent studies suggest that D3 can be up to three times more effective in raising the vitamin D level quickly and staying longer.
How Much Vitamin D Do You Need?
How much vitamin D you need depends on your age and risk factors. The recommended dietary allowance is 600 IU per day for adults up to 70, and 800 IU for ages 71 or older. Some researchers have suggested much larger doses of vitamin D for a variety of health benefits, but too much may harm you. Above 4,000 IU per day, the risk for harm increases, according the Institute of Medicine.
Daily Dose for Breastfed Babies
Breast milk provides multiple benefits for babies, but it is not a good source for vitamin D. The American Academy of Pediatrics (AAP) recommends that all breastfed babies receive a 400 IU daily supplement of vitamin D starting shortly after birth and continuing until the baby is weaned and drinking at least 1,000 mL of vitamin D-fortified formula or whole milk. The upper limit is 1,000 IU for babies 0-6 months old and 1,500 IU for babies 6-12 months old.
Vitamin D for Older Children
Children may be able to get the vitamin D they need for growing bones through foods, including those fortified with vitamin D, such as milk. Beginning at the first birthday, the recommend dietary intake is 600 IU. Supplements are an option to be sure your child gets enough vitamin D, but it's important not go overboard. The upper limits are 2,500 IU for ages 1-3, 3,000 IU for ages 4-8, and from age 9, 4,000 IU.
Testing for Vitamin D
There is a simple blood test – the 25 hydroxyvitamin D test -- your doctor can order to check your level of vitamin D. Current guidelines indicate that you're getting enough vitamin D to keep your bones healthy when your blood level is 20 nanograms per milliliter (ng/mL) or higher. Research is ongoing to understand how vitamin D levels in the bloodstream may affect other aspects of health.
Vitamin D and Other Drugs
Steroid medications can interfere with metabolism of vitamin D. If you take steroids, you should discuss vitamin D with your doctor. The same is true for the weight loss drug orlistat, some cholesterol-lowering drugs, and seizure drugs such as phenobarbitol. Cholesterol-lowering statins, on the other hand, will raise vitamin D levels.
How Much Is Too Much?
There is an upper limit to how much vitamin D you can safely take. The Institute of Medicine recommendations for adults say that a daily intake of up to 4,000 IU of vitamin D is safe. Taking more than 10,000 IU per day can cause kidney and tissue damage. The best approach is to check with your health care provider before taking vitamin D supplements.
More Reading on Nutrition
- The Truth About Vitamin D
- Are You D Deficient?
- Higher Vitamin D, Better Aging?
- Foods Rich in Vitamin D
- Multiple Benefits of D for Women
- The Sunshine Vitamin Catch 22
- Expert Exchange: Osteoporosis
- Video: Vitamin D and Body Fat
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