Vitamin Information Center

Over the past few years the sun has gotten a bad rap. Too much sunshine can put you at risk for skin cancer. And an overdose of sun can also lead to nasty sunburns, or even heatstroke.

But the sun isn’t always bad for the body. Scientists have known for years that the sun is a great source of vitamin D. This vitamin naturally boosts the immune system, your body’s defense against disease. Now mushrooms bathed in ultraviolet (UV) light — like that from the sun — can help you get some of this valuable vitamin.

Each year there are more and more studies released that suggest if you want to be healthy, vitamin D is where it’s at. Vitamin D strengthens your heart and bones, and can prevent asthma and some forms of cancer and diabetes.

Some foods, like fish and eggs, are naturally brimming with the vitamin. And others, like milk and some cereals, are fortified with vitamin D. But you would need to consume a lot of milk and cereal to get your daily dose of vitamin D. Sunlight still reigns king as the best source for vitamin D.

Recently scientists have shown that specially treated mushrooms could give people a vitamin D boost. U.S. Department of Agriculture researchers in California treated portabella mushrooms to suntanning sessions of up to 18 minutes. The mushrooms didn’t develop a bronze glow or complain of heat stroke though. Instead each mushroom produced nearly 4 micrograms of vitamin D per gram of tissue. When white mushrooms were given similar sun treatments, these fungi boasted extra vitamin D, too. Now both kinds of vitamin-infused ‘shrooms are on the market. So if you like mushrooms, you could munch your way to a higher daily dose of Vitamin D.

Depending on a person’s age, people should get between 5 and 15 micrograms (or 200 to 600 international units) of vitamin D each day. Without these amounts, people are prone to get diseases like rickets, which causes distorted, soft bones. These numbers, though, are really just a minimum. Now some scientists suggest it’s better to get as much as five times the recommended vitamin D dose each day.

Having more foods with Vitamin D is a good thing, since there are also several factors that make it hard to get enough of the vitamin from just the sun.

One factor influencing elderly people’s vitamin D intake is that they often spend less time outdoors. Therefore, they need more vitamin D in their diet. And if you spend a lot of your time indoors, playing video games or on the computer, you may need extra vitamin D from your food, too.

Skin color and weight also help determine a person’s vitamin D needs. Darker skin filters out more of the sun’s UV light, so people with darker skin need more sun exposure to make necessary amounts of vitamin D. For unknown reasons, heavier people also need a greater amount of UV light to enable vitamin D production.

And latitude — how far north or south you live — can play a major role in the sun’s ability to help you get adequate vitamin D amounts. As you get farther away from the equator, the amount of UV-filtering atmosphere increases. This means that at higher, more northern latitudes, people get less UV rays. So, if you live in a state like Alaska, most of the year you can’t get enough sun to trigger the vitamin’s production by your skin.

Eating foods enriched with vitamin D or taking a daily vitamin may not be as satisfying as breaking out your bathing suit and lying in the sun. But the right foods and supplements can help keep you healthy until summer’s rays are here again.

Mothers everywhere probably will not be surprised to hear that they were right. Drinking your milk is, of course, good for you. Not only is milk chock-full of calcium, most milk has been fortified with vitamin D — and both nutrients are necessary for good bone health, among other things. And in recent years, a growing body of research has caused experts to conclude that many adults, particularly those over 50, are not getting enough calcium or vitamin D, says Dr. Michelle Germain, a part-time faculty member in the Department of Gynecology and Division of Urogynecology at Greater Baltimore Medical Center.

What is vitamin D?

Vitamin D is a fat-soluble vitamin. It is absorbed from food through the GI [gastrointestinal] tract and also is made by the body. The body needs it because it helps with absorption of calcium and phosphorus, both of which the body needs for bone health.

You said that, in addition to absorbing vitamin D from food, the body also manufactures it. How does the body make vitamin D?

The skin manufactures the vitamin D with the help of ultraviolet rays from the sun. So you need sun exposure to make it. Once we have vitamin D in our bodies, the liver and the kidneys convert the vitamin D into the active form that is used for bone health.

What foods contain vitamin D?

Cod-liver oil is the best way to get vitamin D, but we don’t see many people taking that these days. So other really great sources of vitamin D are fish, such as salmon, mackerel and tuna, and vitamin D-fortified foods, such as dairy products and cereals.

What happens if we don’t get enough vitamin D?

You can become vitamin D-deficient. Children can develop “rickets,” in which the bone doesn’t properly mineralize, and the children develop very soft bones and deformities of their skeleton. In adults, too little vitamin D can lead to osteoporosis. [Too much vitamin D, on the other hand, can make the intestines absorb too much calcium.]

How pervasive is rickets?

In developed countries like the United States, it is pretty uncommon because we fortify so many foods with vitamin D. But there has been a resurgence of rickets in African-American infants and children in poorer states, especially in the South such as Tennessee and Mississippi. The resurgence is being caused by poverty and poor nutrition. It also has to do with darker pigmentation of the skin, which converts sunlight less effectively into vitamin D.

Rickets also is more prevalent in immigrants from Africa, the Middle East and Asia because of their diets before they arrive in the United States and because they may not have enough money to afford good nutrition once here. Again, if they have darker skin, they are not converting UV rays into vitamin D as effectively as people with lighter skins.

Are there other populations for which vitamin D is particularly important?

Older women. If older women are vitamin D-deficient then they are at increased risk for osteoporosis. This is of special concern for menopausal women because once their estrogen levels drop, they begin to lose bone. The vitamin D is necessary to absorb calcium and utilize it in bone formation. And people who have any kind of gastrointestinal illness like Crohn’s disease or celiac disease or any kind of liver disease also are at increased risk for vitamin D deficiency.

Are there any symptoms of vitamin D deficiency that might occur before bone loss?

Unfortunately, there are really no symptoms of it until you are diagnosed with osteoporosis.

What do you tell your patients about vitamin D?

Children and young adults need to consume a diet that is rich in vitamin D-fortified foods. At least 15 minutes of exposure to sunlight twice a week should be adequate to make sufficient amounts of vitamin D. But I also tell them that if you put on sunscreen with an SPF greater than 8, it can interfere with making vitamin D, so diet is very important. Particularly in winter, they should concentrate on eating a diet with plenty of vitamin D-rich foods.

What do you tell adults?

If a woman has osteoporosis, she should ask the doctor if she is potentially vitamin D-deficient. Very often, after a woman has a hip fracture, we check her vitamin D level, and it turns out to be ridiculously low. So, if you have osteoporosis or a fracture, ask about your vitamin D level.

How much vitamin D do we need?

Last year, the National Osteoporosis Foundation released new recommendations about vitamin D. The National Institutes of Health also are due to release this spring new guidelines. According to the National Osteoporosis Foundation, adults under age 50 need 400 to 800 IU [International Units] of vitamin D3 daily. [Also called cholecalciferol, vitamin D3 is the kind of vitamin D that best enhances healthy bones.] And menopausal women and adults over the age of 50 need 800 to 1,000 IU of vitamin D3 daily.