In search of essential vitamin D


Dear Doctors: I’ve heard that a lot of people don’t get enough vitamin D in their diet. What about getting it from the sun? Is that too risky? Also, what happens if you don’t get enough?

Dear Reader: Vitamin D is a fat-soluble nutrient that our bodies require in order to absorb calcium from the intestines. That calcium is then used to harden the tissues of the skeleton, a process known as mineralization. Vitamin D is also crucial to bone growth, plays a role in managing inflammation, helps prevent involuntary muscle spasms and aids in the regulation of blood phosphorus levels.

Not getting enough vitamin D makes it difficult to maintain adequate levels of calcium and phosphorus, which can cause bones to gradually become thin and brittle. Together with calcium, vitamin D also helps protect older adults from osteoporosis. In children, a lack of the vitamin can lead to rickets, a disease that interferes with mineralization. Rickets is a sometimes painful disease, marked by poor skeletal formation and soft, weak bones that can become malformed.

When our skin is exposed to sunlight, our bodies become natural vitamin D factories. The energy in ultraviolet rays triggers a complex chemical reaction that, along with help from the liver, kidneys and certain cellular structures, results in the formation of vitamin D. The nutrient is also naturally available in fatty fish, including tuna, mackerel, salmon and sardines, and in smaller amounts in certain foods such as beef liver, cheeses, egg yolks and some mushrooms. However, we don’t eat these foods in large enough quantities to satisfy our body’s ongoing need for vitamin D. To help make up for a potential deficit, a range of prepared foods are fortified with the nutrient. These include orange juice, breakfast cereals and dairy products, as well as some soy, rice and noodle products.

Elizabeth Ko, MD and Eve Glazier, MD

The amount of vitamin D that you need to maintain optimal bone health depends on your age. Infants up to 1 year old should get 400 international units (IU) per day. Children, teens and all adults up to the age of 70 are advised to get 600 IU. After age 70, when our bodies become less efficient, the recommendation increases to 800 IU per day.

It’s rare, but possible, to get too much vitamin D. The addition of the nutrient to prepared foods is carefully regulated, and our bodies naturally limit the amount they manufacture from sun exposure, so you’re not going to run into problems there. If you’re going to rely on vitamins or supplements for your vitamin D intake, be sure to check with your health care provider.

Getting enough vitamin D from the sun depends on location, weather and skin type. Also, sunscreen limits how much a person can produce. For those with light skin, 15 to 30 minutes of full sunlight on bare arms, legs or torso a total of two to three times per week is adequate. Due to the protective effects of melanin, darker skin requires longer exposure. People with any kind of skin cancer history or risk should rely on diet and supplements to get their daily allowance.

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