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Warning: Sunbathing May Be Addictive

While you were basking on the beach, researchers have been trying to figure out why it is so hard to convince people to break the skin cancer-causing sunbathing habit. One theory: ultraviolet (UV) light can be addictive. Some studies have found that giving an opiod blocker to frequent tanners produced withdrawal-like symptoms, results that imply, but don't necessarily prove, that opiod pathways and reward centers in the brain are involved in their tanning activities. The latest evidence in support of the UV addiction theory comes from a study with mice at Massachusetts General Hospital. Researchers there exposed a group of lab mice to a daily dose of UV light equivalent to the exposure of fair-skinned humans to 20 to 30 minutes of midday Florida sun. The dose was calibrated to tan, but not burn, the shaved backs of the mice. Within a week of daily exposure, feel-good beta-endorphin levels in the mice’s blood increased significantly, and didn’t drop until the UV exposure ended. When treated with a drug that blocked the opiod effect, the critters went into mouse withdrawal, complete with shaking and teeth chattering.

Sources:
David E Fisher, et al, ”Skin β-Endorphin Mediates Addiction to UV Light,” Cell, doi.org/10.1016/j.cell.2014.04.032

The Early Bird Stays Slim

If you’re watching your weight, you might consider getting up early and going outside. A new study from Northwestern University’s Feinberg School of Medicine showed that people whose exposure to bright natural light was mainly early in the day – between 8 a.m. and noon – had a lower body mass index than people whose light exposure occurs mostly in the late afternoon. All told, the difference in weight between early birds and not-so-early types could be as much as 30 pounds, stemming entirely from the influence and timing of their light exposure, the study found. The Northwestern researchers recruited 54 people, average age 30 who wore wrist monitors that tracked their light exposure and sleep time for a week. The study participants kept logs of what they ate and how often and how much they exercised. The researchers said that the light exposure could come from various sources, including through car windows. Bright light later in the day or at night has the opposite effect – it has been linked to obesity.

Sources:
Phyllis Zee et al, “Timing and Intensity of Light Correlate with Body Weight in Adults, PLOS One, DOI: 10.1371/journal.pone.0092251

Vitamin D: Are You Deficient?

Vitamin D deficiency is common in the developed world, and according to at least one study, people with very pale skin are most likely to be seriously deficient. Researchers at the University of Leeds in the United Kingdom took the vitamin D levels of about 1,200 people. They found that 730 had lower than optimal levels, and those with fair skin had significantly lower levels. The possible reason? People with very fair skin tend to avoid the sun because they burn easily, making it difficult for their bodies to make sufficient "D" from sun exposure. This suggests that if you have fair skin and tend to avoid direct sunlight, supplementing may be especially important for you.

Regardless of your skin color, humans need vitamin D to facilitate bone mineralization, as well as for protection against a number of serious diseases. You can get vitamin D through foods such as full-fat cheeses and plain yogurt, eggs, salmon, tuna and mackerel. For people with pale skin, seniors (the ability to synthesize vitamin D decreases with age) and anyone who isn’t getting enough vitamin D through food and sun, I recommend 2,000 IU of vitamin D daily in the form of D3 (cholecalciferol) rather than D2 (ergocalciferol).