Going outside is something most of us take for granted. We don’t really think of going outside as something that can impact our health. But there’s no doubt that it’s something our ancestors did for eons up until recently.

This isn’t to say that people don’t go outside every day. With few exceptions, everyone goes out for some period of time every single day. However, some of us may not do it nearly enough, and this likely has a negative impact on our health.

Everyone can get behind the idea that going outside is important for vitamin D production. When ultraviolet radiation(UVR) hits our skin, specifically UVB rays, our skin produces vitamin D from cholesterol. Unfortunately, for most people, this is the extent to which going outside benefits our health.

On the other hand, UVR has it’s dark side. Excessive burning due to UVR causes skin cancer, and UVA radiation speeds up the aging process in the skin. As a result, many people not only avoid the Sun, they slather on sunscreen to block UVR from hitting the skin when they do go outside.

This may be a colossal mistake. As it turns out, UV exposure to both the skin and the eye seem to play an important role in our physiology. Consequently, eliminating UVR by staying indoors, always wearing sunscreen, and wearing sunglasses that block it may have a negative impact on our health.

Going outside: How UVR impacts physiology

Human physiology is extraordinarily complex. Unfortunately, we often take a very myopic stance towards things that harm us. Often, this does more harm than good.

A great example is how we’ve largely viewed bacteria up until very recently. Twenty years ago, bacteria were bad mofos. So when we found it, we blew it up with an antibiotic. As a result, taking antibiotics was largely viewed as having little downside.

Then, of course, we found out our internal environment isn’t really all that sterile. Moving forward, we found that we are literally teeming with bacteria, many of which provide vital functions to our health. As such, tossing down broad-spectrum antibiotics willy-nilly has substantial drawbacks to people who do it on a regular basis.

We currently do the same with UVR. Many doctors. particularly dermatologists, view UVR as something with no physiological value to us. Instead, it’s a stressor and carcinogen that should be strictly avoided.

On the other hand, research into this area doesn’t really support this notion. UVR has beneficial effects independent of the production of vitamin D, and the most supported stance is that some is good, too much is bad, and there may potentially be a minimal dose we need daily to be healthy.

A recent review covered the many ways that UVR benefits our health. Here are just some of the ways that exposure to UVR impacts our physiology.

UVA exposure lowers blood pressure

Our skin contains stores of metabolites of nitric oxide(NO). When our skin is exposed to UVA radiation, these metabolites are released as NO, causing an increase in vasodilation.

To put it another way, it causes our blood vessels to open up and accommodate more blood. Consequently, this has a lowering effect on our blood pressure which decreases our risk of cardiovascular disease and stroke

Given that cardiovascular disease and stroke are the 2 leading causes of death around the World, this is definitely something to consider. The best thing about this is that you can get UVA exposure during the early morning and late afternoon/evening hours when total UVR is lower.

In other words, you can get exposure during periods when the risk for burning is very low.

UVR has an anti-inflammatory effect

Exposure of the skin to UVR may also play an important role in regulating the inflammatory response. Release of NO can also have anti-inflammatory effects, as can many other metabolites released from irradiated skin.

Another interesting anti-inflammatory candidate is carbon monoxide(CO). Most of us think of the toxicity of carbon monoxide, but it’s released in low levels from nearly every cell in our body every day.

In reference to the skin, exposure to UVB upregulates a stress responsive pathway known as HO-1. This causes the release of carbon monoxide which, in addition to having an anti-inflammatory effect, is essential to our circadian rhythms.

We covered this in a blog you can check out here.

UVR plays a role in central hormonal signaling

When most people think of human physiology and what makes us go, they think of the various hormones and neurotransmitters that help us cope with the environment. Thinks like:

• Cortisol
• Thyroid hormone
• Catecholamines(epinepherine/norepinepherine)
• Cytokines
• Serotonin
• Acetylcholine
• Histamine
• And so on

Interestingly, our skin has fully functional neuroendocrine circuits that mirror the central circuits. In other words, the skin has a fully functional HPTA axis(Hypothalamic-pituitary-thyroid-adrenal axis).

The skin and brain share a bi-directional axis with one another via the autonomic nervous system. Furthermore, animal models indicate that exposing both the eye and skin to UVR has effects on the central HPTA axis.

Finally, some of the local hormones shared with central neuroendocrine circuits may enter the blood to exert systemic effects. Since these are stress-responsive pathways, it makes sense that local and systemic effects to stress are coordinated.

From a circadian perspective, exposure to stress happens across all systems during the active period. Coordinating stress responsive pathways to “turn on” during these times more than likely imparts a survival advantage.

However, human clinical trials for these effects are not plausible at this time.

Going outside and gut health

Regularly heading outside for a walk or hike may also provide benefits to gut health. We covered many of these effects due to UVR in a blog you can check out here. In addition, exposure to more microorganisms in the outdoor environment is believed to play a role in the greater diversity of the modern day hunter gatherer microbiome compared to humans living a modern lifestyle.

On top of this, there is an indirect link between Sun exposure and gut health via a hormone called alpha melanocyte stimulating hormone(a-MSH). The primary role of a-MSH is to stimulate the production of melanin by melanocytes in skin.

Melanin is the pigment in skin generated from exposure to ultraviolet light. Melanin protects DNA in skin cells by providing a barrier to absorb UVR so that it can’t damage DNA. However, a-MSH also has systemic effects that come from exposing the eye to UVR.

Released from the pituitary, this a-MSH stimulates melanocytes in skin to produce melanin, but also plays a role in the immune system. Furthermore, a-MSH stimulates the expression of orexin, a hormone that controls arousal, wakefulness, and appetite.

Orexin also has roles in the gastrointestinal system. Recent evidence indicates that aberrant orexin signaling may promote IBS by increasing visceral hypersensitivity. In addition, orexin appears to play a role in gastric acid secretion, motility, and may improve intestinal barrier function.

Going outside has other benefits

Though we’ve only covered the physiological benefits of going outside as it pertains to exposure to UVR, there are other benefits to going outside. Forest bathing is considered a good practice for improving mental well-being, as is gardening.

Both of these practices impart beneficial effects, likely through a combination of psychological effects as well as the above-mentioned physiological ones. But, as discussed, well-controlled clinical trials are not currently plausible.

This requires us to lean on the epidemiological data, which generally shows a beneficial effect on various health markers with increased Sun exposure. Most recent papers tend to show decreased mortality risk with increasing Sun exposure(Link, link, link). Other evidence indicates that greater sun exposure is protective against inflammatory bowel disease in adults and children.

It’s important to point out the nuance in this discussion. Just because exposing yourself to the Sun has a beneficial effect on health doesn’t mean overdoing won’t give you skin cancer or cause other problems.

But given that there does appear to be important physiological effects from Sun exposure and being outside, strict avoidance is a bad idea too.

Conclusion

Many aspects of our modern lifestyle have a negative effect on our health. We are more sedentary, eat too much processed food, are exposed to stress 24/7, are socially isolated, and disconnected from nature. As a result, we are suffering from diseases of a chronic nature.

This takes both a physical and emotional toll on us. There are very few things we can do for our health on a daily basis that are ultra-low risk with a potentially huge payoff. Going outside into nature is one of those things, provided we approach it in a sane and rational way.

While we focused on the physiological effects of UVR in this blog, there are other reasons to go outside. The sights, the sounds, and escapism that come from connecting with nature have seemingly robust effects on our health. This has led to a concept known as the Nature Pyramid put forth by Tanya Denckla-Cobb from the University of Virginia, depicted here:

Make an attempt to improve your health by reconnecting with nature using the Nature Pyramid as a guide to meeting your nature needs.