The good sun: too much sun can be bad for human health. So can too little

Kirsten Weir
http://www.findarticles.com/p/articles/mi_m0BFU/is_16_89/ai_n6110170/print

Several years ago, an Ohio mother was arrested and thrown in jail for endangering her three young children. Her crime? She let the kids become sunburned while spending the day outdoors at a county fair.

The charges against her were eventually dropped, but the message was clear: The sun is dangerous! "Everybody always hears this message that sunshine is really bad for you," said Michael Holick, a professor of medicine at Boston University. Holick argues that there is more to the story. In moderation, he says, sunshine keeps us healthy.

SAD

Sunshine clearly has the power to lift our moods; most people feel good when they're outside on a bright sunny day. During the gray winter months, some people even suffer from a type of depression called seasonal affective disorder (SAD). But sun has health benefits that go beyond the psychological.

Sunshine stimulates the production of vitamin D in the body. Vitamin D, also known as calciferol, is found in foods such as salmon and eggs. But ultraviolet (UV) radiation from the sun is an even more important source. UV radiation is electromagnetic radiation invisible to the naked eye with a wavelength just shorter than that of visible violet light. When one type of the sun's UV rays, called UVB, hits the skin, it triggers a chemical reaction that produces vitamin D. (See "Let the Sunshine In.")

SUPER VITAMIN

Why is vitamin D important?

It helps the body absorb the element calcium, which is necessary for healthy bones. Babies and young children who don't get enough of the vitamin can develop rickets, a disorder marked by a softening and weakening of the bones.

Several recent studies have shown that vitamin D is important for other reasons as well. "Every cell in the body recognizes vitamin D," Holick said. "It regulates hormones, It he immune system, normal cell growth, and decreases cancer cell growth."

A shortage of vitamin D has been linked to type 1 diabetes, a disease that usually develops in childhood and prevents the body from processing sugar in the blood normally. A study in Finland found that young children who received vitamin D supplements through adulthood were 80 percent less likely to develop type I diabetes than children who didn't take the vitamin, says Holick.

Recently, Holick studied the effects of UV light on patients who have hypertension, or high blood pressure. He found that periodic visits to tanning beds for a dose of UVB worked as well as prescription medication in lowering patients' high blood pressure.

Vitamin D deficiencies have also been linked to multiple sclerosis, a disease that attacks the nerve cells and affects bodily functions and movement, as well as rheumatoid arthritis, which causes pain, swelling, and stiffness in the joints.

CANCER KILLER

Researchers have also found evidence that vitamin D may help prevent some common types of cancer, including breast, ovary, colon, and prostate cancers. Cancer occurs when abnormal cells proliferate (multiply) out of control. Vitamin D appears to put the brakes on that process.

Here the story gets tricky because UV light is famously responsible for causing cancer. Skin cancer is the reason we're bombarded each summer with messages about the evils of sunlight. When UV rays burn the skin, they can damage DNA, which may lead to skin cancer.

Fortunately, the most common types of skin cancer are easily treatable. One type, malignant melanoma, can be deadly if left untreated. According to the Centers for Disease Control and Prevention, melanoma kills about 8,000 Americans annually. Holick estimates that many times that number are dying from other types of cancers because they aren't getting enough vitamin D. "One hundred and fifty thousand Americans could be saved each year by exposure to sunlight," he said.

SUN SMARTS

Certainly, no one is recommending that we all ditch the sunscreen and hit the beach. Holick agrees that sunburns are bad for you, but, he argues, some sun exposure can be healthy. He and his colleagues recommend limited, unprotected exposure to the sun, which can mean just five to ten minutes of sun a day for a light-skinned person in the summer. Dark-skinned individuals may need 25 minutes, because they make vitamin D more slowly.

In the winter, especially in northern areas, getting enough vitamin D from the sun can be difficult. Even in summer, many people never leave the house without sunblock, which keeps UVB rays from doing their job. "Parents always slather their kids with sunscreen," Holick said.

Holick's recommendations are very controversial. Many dermatologists argue that taking a multivitamin is a safer way to reap the positive effects of vitamin D without the risk of skin cancer. But a typical multivitamin contains 400 international units (IU) of vitamin D, and doctors now recommend about 1,000 IU each day. Holick believes that many people won't go to the trouble of finding higher-dosage vitamin D pills in addition to their daily multivitamin.

Holick suggests going outside and letting the sun do its work. "If you're going to go out for ten minutes," he said, "don't bother with the sunscreen."

LET THE SUNSHINE IN

How your body makes vitamin D from sunlight.

1. Incoming UVB rays from the sun are absorbed by the epidermis, or outermost layer of skin.

2. Skin cells called keratinocytes convert cholesterol molecules to a chemical called previtamin D3.

3. When our bodies need vitamin D, our kidneys make it from the previtamin.

Objectives

New research indicates that sunshine has important benefits for human health.

Critical Thinking

* Type 1 diabetes, multiple sclerosis, and rheumatoid arthritis are all autoimmune diseases, diseases in which the body's own immune system attacks its tissues. How might vitamin D play a role in preventing such diseases?

National Science Education Standards

* Earth in the solar system: solar radiation

* Personal and community health: disease prevention

Internet Links

* Nature." Vitamin D Health Benefit Boon ?: http://www.nature.conffnsu/0401121 040112-2.html

Nutrition Action Healthletter: Soaking Up the D's: http://www.findarficles.com/cf_0/m0813/ 10_30/111356934/p1/article.jhtml

Fill in the blank

1. -- the most dangerous form of skin cancer, kills about 8,000 Americans each year.

2. Vitamin D helps the body absorb --, an element necessary for healthy bones.

3. High blood pressure is also known as

4. -- radiation is invisible electromagnetic radiation from the sun, with a wavelength just shorter than that of violet light.

5. Vitamin D is also known as --.

6. -- is a soft-bone disease caused by a lack of vitamin D.

7. Rheumatoid -- causes pain, swelling, and stiffness in the joints.

8. Doctors now recommend that people consume -- international units of vitamin D each day.

The Good Sun

1. Malignant melanoma, 2. calcium, 3. hypertension, 4. Ultraviolet, 5. calciferol, 6. Rickets, 7. arthritis, 8. 1,000

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