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Why Are Humans So Drawn To Sunlight Despite Its Negative Consequences?

Sunny-beachIt doesn’t make sense: If sunlight causes cancer, why are human beings so drawn to it, flocking to sunny beaches for vacation time and hoping for sunshine after a rainy spell?

One answer, says David Fisher, chief of dermatology at Harvard-affiliated Massachusetts General Hospital in Boston, may be that humans are literally addicted to sunshine so our skin can make vitamin D. New evidence suggests that we get the same kick out of being in the sun that we get from any addictive substance or behavior. It stimulates the so-called “pleasure center” in the brain and releases a rush of feel-good chemicals like endorphins.

So there may be more than a desire to look good in a tan behind the urge to soak up the sun’s rays. This craving may be a survival mechanism that evolved over thousands of years because humans need vitamin D to survive. Skin makes this crucial vitamin when it is exposed to sunlight. There isn’t much vitamin D in food (except in some of today’s fortified foods) so the human brain rewards us with a rush of pleasure when we seek out the sun and get vitamin D.

Seeking sunshine can be downright dangerous. As Fisher points out, the ultraviolet (UV) radiation from sunshine is “the most ubiquitous and common carcinogen in the world.” Skin cancer is the most preventable form of cancer simply because we know what causes it: sunlight. Yet despite this knowledge, skin cancer is on the rise, increasing faster than any other form of cancer.

Avoiding D-ficiency

A simple blood test at your doctor’s office can determine if you are deficient in vitamin D. New guidelines from the Institute of Medicine recommend 600 international units (IU) of vitamin D a day for everyone between the ages of 1 and 70, and 800 IU for those over age 70. Some experts argue that this isn’t enough, and that five to 10 minutes a day outdoors without sunscreen is a reasonable way to get some natural vitamin D. (If you live north of a line connecting San Francisco with St. Louis and Richmond, Virginia, don’t bother doing this between November and March—the amount of ultraviolet light hitting your body won’t be enough to generate vitamin D.)

If you’ll be out longer than five to 10 minutes, cover up. Use sunscreen but understand that the evidence for its long-term protection against skin cancer is “changing rapidly,” says Fisher. Some newer studies show no benefit, some even show elevated risk for people who use sunscreen. More effective protection is a full-brimmed hat and long sleeves and pants. Best choice, says Dr. Fisher, “Stay in the shade.” Kay Cahill Allison

For more on caring for your skin, treating age-related skin conditions, and skin rejuvenation, check out the Harvard Health Publication’s Special Health Report: Skin Care and Repair.


Kay Cahill Allison’s biography can be viewed here.

*This blog post was originally published at Harvard Health Blog*

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3 Responses to “Why Are Humans So Drawn To Sunlight Despite Its Negative Consequences?”

  1. Norman Smith says:

    A blood test cannot determine the amount of stored fat-soluble vitamins or what are normal levels for these vitamins. The growing number of people with health problems for industrialized nations highlights the quality differences in the food versus non-industrialized nation. The use of petroleum-based fertilizers disrupts the microbial ecology of the land and the result is a crop that produces lower amounts of minerals and vitamins than the wild-type plant. The U.S. began using this type of fertilizer in 1913. The first sign of a problem was the dust bowl of 1933 but the decrease levels of vitamins in the food was undetected. This problem has been insidious and has increase in severity with each generation because the first dose of fat-soluble vitamins occurs in the womb and the last dose from breastfeeding thus creating a generational downward step. For perspective, there is the growing number of younger people with health problems, the need for more vaccines in children, and the heavily medicated elderly (critical low levels of fat-soluble vitamins). Tracing the molecular pathway of diseases and infections there is always one or more fat-soluble vitamins involved or the under expression of its functions. As for the debate about an inactive fat-soluble vitamin causing harm, there is no upper limit. The body regulates fat-soluble vitamins intake, metabolism, and storage. To highlight fat-soluble vitamins importance to human health, it drove evolution to develop storage cells because source is seasonal and the environmental factors are constant.

  2. asdf says:

    Or…it could be that the sun is the very reason for our existence…it is essentially our only visible God

  3. asdf says:

    Or…it could be that the sun is the very reason for our existence…it is essentially our only visible God

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