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Eighty years ago, when sun exposure was first associated with skin cancer, popular culture was exalting tanning by emphasizing that a “fine brown color suggests health and good times and is a pleasant thing to see.”
We know that sun exposure can be deadly and today’s public awareness campaigns strongly focus on sun avoidance to prevent skin cancer. But we also know that sunlight is important to our health and plays a role in many biological processes in our bodies.
In fact, some physicians and scientists are taking a closer look at sunlight to expose the lesser known benefits of ultraviolet (UV) light.
What is UV Light?
When we are talking about the dangerous component of sunlight, we are really talking UV light. UV light is ionizing radiation, meaning that it frees electrons from atoms or molecules, causing chemical reactions. UV light is divided into three categories listed in order of increasing energy: UVA, UVB, UVC.
UVC is the most harmful, but the ozone layer and other components of the atmosphere filter all of it out before it reaches us. That’s also the case for a large percentage of UVB light. But nearly all UVA light reaches the Earth’s surface.
Both latitude and season play large factors in our individual exposure to UV radiation. Countries farthest from the equator during winter months receive the least amount of UV radiation, while equatorial countries receive the most.
UV Light Causes Chemical Reactions in the Body
Unlike visible light, the energy from UV radiation can be absorbed by molecules in our body, causing chemical reactions. When the energy from UV radiation is absorbed by DNA, it can cause reactions that lead to genetic mutations. Some of these mutations can lead to the development of skin cancer, which is the most common cancer in the U.S. Basal cell carcinoma, squamous cell carcinoma and malignant melanoma (one of the deadliest cancers) are all associated with UV light exposure.
However, not all chemical reactions that UV light induces are harmful. In fact, some of them are beneficial. For instance, we can get vitamin D from eating certain plants and animals, but a main source of vitamin D comes from exposure to UV radiation.
Vitamin D is critical to maintaining bone density by increasing calcium absorption in the gut. Chronically low levels of vitamin D can lead to osteoporosis. Apart from its effects on bone, vitamin D has also been shown to improve balance and muscle strength in the elderly, which decreases the number of falls leading to fracture.
UV light induces the body to synthesize other molecules as well, including opioid-like molecules thought to cause a tanning “high.”
UV Decreases Cancer Mortality
Research suggests that the risk of developing lung, prostate, breast, colorectal and pancreatic cancer may be decreased by sun exposure. This protective effect against cancer is most pronounced in sunny countries. While smaller studies of colorectal and prostate cancer have conflicted with this finding, many studies support a beneficial relationship between sun exposure and internal cancers and it has been suggested that the risks associated with sun exposure may be outweighed by its ability to prevent certain types of internal cancers.
Sunlight may also improve cancer outcomes. The prognosis for patients diagnosed in summer and fall is better than those diagnosed in winter and total sun exposure prior to diagnosis is a predictor of survival.
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