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Here on the 41st parallel, it’s late August, and the days are noticeably shorter. The daily Ultraviolet Index forecasts I get from the Environmental Protection Agency also reflect the waning of summer as the peak UV levels are starting to decline. 

What this means for maximizing the health benefits of sunlight is that I can spend more hours during the morning and late afternoon in direct sunlight without getting potentially damaging levels of ultraviolet (UV) radiation.

Not to minimize the realities of sunlight induced skin damage, but getting some level of UV radiation, especially UVB (wavelengths 280-340 nm), is critical to the health of our bones, and possibly to the health of our immune system, through the production of vitamin D in the skin. Sunscreen blocks UVB and vitamin D production. Because people of color have more melanin in their skin, and melanin reflects UVB, up to 4 times more UVB is needed to produce health sustaining levels of vitamin D than for white people.

Given the growing number of research studies demonstrating vitamin D receptors in many different parts of the brain, we may soon learn that Vitamin D also affects mood and nervous system health.

One of the paradoxes, or yet to be untangled puzzles, of sunlight, UV radiation and health is that low to moderate intensity UV may actually protect against skin cancer if there is a slow, gradual increase in UV levels.

The mechanisms for this emerging potential protective effect of low-moderate intensity UV are several. First there is the simple UV reflective effect of melanin, which increases skin pigmentation, or tanning, in response to gradual increases in UVB. Second, human skin contains all the component parts needed for melatonin synthesis (yes, the same melatonin that helps regulate sleep and circadian rhythms), and laboratory studies have shown that melatonin can inhibit the development of cancerous tumors. The catch is, production of skin-based melatonin seems to require prior, gradual exposure to bioactive (ie low to moderate) levels of UVB radiation.

The pattern I see across these studies is that low to moderate levels of UV radiation from morning and late afternoon sunlight trigger built in mechanisms that help protect against the damaging effects of higher intensity UV radiation. Sunlight is much more damaging when we expose ourselves to sudden, dramatic increases in exposure - like going from being an office mole to a vacationing beach bum in one day, or like spending an entire weekend day in direct summer sun when all your weekdays are spent indoors.

So, here is my approach to maximizing the health benefits of sunlight:
During summer, I try to get as much early morning and late afternoon sunlight as I can.
I use EPA UV Alerts (sent daily to my email and calculated specifically for my geolocation) to be aware of days when UV intensity is going to be high and when UV starts to trend down. Because I think the balance of research shows that moderate intensity (ie bioactive) UVB is beneficial to health, I’m more liberal about my exposure to mid-range UV, but when the UV Index is forecast to be above 7 or 8, I heed their precautions.

When I’m outside during midday in the summer, I stay in the shade as much as possible.

I avoid prolonged direct midday summer sunlight, especially if I haven’t been able to get much morning or late afternoon sun during the prior few days.

If I’m going on a trip during which I’ll be getting a lot more sun exposure, like if I’m going to climb a 14er or going on a sun and sand vacation, I try to increase my sun exposure where I live for a few days before my departure and gradually increase over my sun exposure over several days when I reach at my destination. This is especially important when traveling to the tropics in winter or early spring (wish I could say I’d done that recently).

During winter I use different strategies to balance the hazards and benefits of UV radiation and sunlight, but I’ll save that list for a later post.

If you take medications or have medical conditions that can affect your sensitivity to sunlight, please talk with your personal healthcare professional before increasing your exposure to sunlight.