We’ll dive into more about that below – plus answers to frequently asked questions and best practices for getting outside – but first let’s look at an overview of the benefits of sunshine.
1. Strengthens & Balances The Immune System
Sunlight strengthens and balances immune function in at least three ways:
UV light stimulates the production of vitamin D
Vitamin D helps regulate “At least 1,000 different genes governing virtually every tissue in the body.”
That may explain why low vitamin D levels are associated with a such a broad spectrum of issues, including impaired immune function, fatigue, bone pain, back pain / general muscle pain, depression, impaired wound healing, rickets and bone loss.
On the flipside, optimal vitamin D levels are associated with healthy neuromuscular function, calcium metabolism, and of course immune function. Unfortunately, more than 40% of US adults are estimated to be vitamin D deficient, so many of us are not receiving the full potential of these benefits.
Sunshine directly activates immune cells via blue light
A specific wavelength of sunlight – blue light – directly activates key immune cells called T lymphocytes, says Dr. JoAnn Manson of Harvard Medical School. Sunlight also increases the motility of T lymphocytes, which is their ability to move around and get where they need to go.
This is a benefit that is thought to be separate from the benefits offered by vitamin D. Interestingly, our skin contains about twice as many T lymphocytes as can be found our the bloodstream, so activating them via sunlight may significantly increase the number of T cells available for mounting an immune response.
Sunlight increases levels of immune regulatory molecules
Sunlight boosts our concentrations of molecules that are thought to support a balanced immune system. In particular, UVB light increases production of regulatory T cells (Tregs), which play a significant role in calming an overactive immune system.
Vitamin D deficiency is also associated with an increased risk of certain autoimmune disease, including multiple sclerosis, irritable bowel disease and type I diabetes. Although the relationship is not fully understood, it may be in part because Vitamin D is an immune modulator that helps our bodies balance between an underactive immune system (increased susceptibility to infection) and an overactive one (autoimmunity).
With that said, sunlight may not be beneficial for certain autoimmune diseases, so if you have one be sure to talk to your doctor about what’s best for your situation.
2. Boosts Mood & Overall Well-Being
Have you ever wondered about the phrase “sunny disposition?” When sunlight enters our eyes, it lifts our mood by stimulating the release of serotonin – often called the Happiness Hormone – along with dopamine and natural opiates called endorphins.
Inadequate sun exposure can cause serotonin levels to drop, and low levels are associated with what some people call the winter blues. Because this particular benefit is triggered by bright light hitting the light-sensing cells in our retinas, it can be simulated using an indoor light therapy lamp.
However, another pretty amazing mood boosting mechanism requires real sunshine. Pigment cells in our skin called melanocytes “express a fully functioning endorphin receptor system,” meaning that when they’re exposed to light they create a “feel good effect” by increasing our levels of endorphins. Kind of amazing, right?
3.Lower Blood Pressure & Heart Health
When UV light touches our skin it triggers the release of nitric oxide – a molecule that relaxes our blood vessels – resulting in lower blood pressure and a reduced risk of heart disease and stroke.
This is especially important when you consider that high blood pressure affects nearly one billion people, and taking vitamin D supplements doesn’t trigger the same release of nitric oxide that sunshine does.
That’s why at the UnIversity of Edinburgh, a Senior Lecturer in Dermatology named Richard Weller and his colleagues “say the effect is such that overall, sun exposure could improve health and even prolong life,” because the blood pressure benefits of moderate exposure outweigh other risks.
4. Deeper, Better Sleep
When our eyes take in the right kind of light at the right time of day, it switches on responses in our bodies that affect not just our emotional well-being, but how deeply we sleep, our metabolism, hormone balance, overall health, and more.
Here’s how Dr. Breus, who is a Diplomate of the American Board of Sleep Medicine, Fellow of The American Academy of Sleep Medicine, and the author of The Power of When, puts it:
In the morning, sunlight comes into your eyeballs, travels along the optic nerve, and activates the SCN to begin each day’s circadian rhythm. The SCN is the master clock that controls dozens of other clocks throughout your body. Over the course of the day, your core temperature, blood pressure, cognition, hormonal flow, alertness, energy, digestion, hunger metabolism, creativity, sociability, and athleticism, and ability to heal, memorize and sleep, among many other functions, fluctuate according to and are governed by the commands of your inner clocks.”
When it comes to sleep specifically, bright light in the morning stimulates the production of serotonin. During the day it benefits our mood, but as night rolls around the body uses it to make melatonin (often called the Sleep Hormone). The more serotonin you have, the more melatonin you make.
That’s a good thing, because in addition to helping our bodies fall asleep at the right time, melatonin helps regulate the immune system, reduces inflammation and supports cardiovascular health.
I’ve covered more about best practices for getting early morning light in this article on science-backed sleep tips. Also, exposure to blue light at night inhibits melatonin production, so I wear blue light blocking glasses if I’m going to watch a movie or spend time on my computer. You can read more about the benefits of blue light blocking glasses here.
5. Improved Cognitive Function
The areas of the brain that are involved in complex planning, processing, and the formation of new memories are the most rich in vitamin D receptors, so it’s no surprise that several studies have found that vitamin D deficiency results in cognitive impairment.
Even getting just a little bit of sunlight can increase alertness, says this study. The improvement was found to correlate to increased activity in the thalamus, which is thought to be a gateway for complex thoughts.
6. Bone Health
In this article published in the UK, it’s noted that many Victorian era diseases are on the rise in some modern areas. One of those is rickets, which is a severe vitamin D deficiency that leads to soft or misshapen bones, restricted growth, bone pain and muscle weakness.
In adults, vitamin D deficiency is thought to play a role in osteomalacia (soft bones) and osteoporosis (reduced bone mass).
While some dietary vitamin D does appear to be beneficial in these cases, some studies have found that high doses actually reduce bone mass over time.
Researchers are not exactly sure why yet, but one possibility is that large amounts of vitamin D may interfere with the absorption of another vitamin that plays a role in bone health – vitamin A.
According to Stephen Levine, PhD, “vitamins D and A are an ancient and inseparable team that evolution has honed through time. They must be supplemented together in order to not create a ‘functional’ deficiency of either one. Excess D will create a ‘relative’ deficiency of A, even when dietary levels are adequate. And vice versa.”
He adds that:
“Vitamin K brings up the rear, like a good third teamplayer, and enhances vitamin D’s impact on bone, and protects against kidney damage from excess D. The top vitamin K expert in this country, Sarah Booth, PhD of Tufts University, speculates that K may also work through the ancient RXR receptor, just like D and A. But that has not been studied yet.
Finally, vitamin E seems to play a role as well, working together with vitamins A and D”
My main source of dietary vitamin D is raw cod liver oil, which contains both vitamins A and D. Vitamin E is found in nuts and seeds, avocados and other whole foods.
Vitamin K2 is found in fermented foods (especially natto) and animal fats like cheese, butter, and eggs. If you have certain beneficial gut bacteria, it can also be synthesized in your digestive tract.
7. Sunlight supports a healthy gut microbiome
When it comes to the bacteria living in our gut, more truly is merrier. Gut microbiome diversity- which is the number of colonies of bacteria and other microbes living in our digestive tract – is associated with a wide range of benefits including immune health, stress resilience, the ability to digest and assimilate nutrients, and even an increase in sociability.
Consuming a wide variety of beneficial microbes via probiotics and fermented foods can increase our microbiome diversity, but according to the University of British Columbia sunlight can, too. In this study, UVB light increased gut microbiome diversity in just one week.
8. Reduces Inflammation
“In the winter, the study found, your blood contains a denser blend of immune responders, while summer veins swim with fat-burning, body-building, water-retaining hormones.” (29)
The immune responders mentioned often include inflammatory molecules, which can be helpful for dealing with pathogens. On the other hand, sunlight triggers “the release of a compound in the skin that dampens inflammation.”
9. May Reduce The Risk of Some Types of Cancer
While excess sun exposure is a risk factor for skin cancer, moderate sun exposure “seems to have a protective effect against the incidence of colorectal, breast, and prostate cancer and non-Hodgkin lymphoma.” Not all types of exposure are considered equally beneficial, though.
This study found that regular exposure (versus intermittent exposure) produced a beneficial effect. It also noted that “Although vitamin D has a strong influence on the effect of solar exposure on cancer prevention, it is not the only explanation for this association, which is not entirely reproduced by nutritional supplementation.”
In other words, taking vitamin D supplements doesn’t seem to fully reproduce the benefits of sunlight. The researchers propose that the effects of sunlight on immune system modulation and circadian rhythm may be playing a role in addition to vitamin D production.
Also, although it seems counterintuitive, safe sun exposure may reduce the risk of melanoma. This study found that “outdoor workers have a decreased risk of melanoma compared with indoor workers, suggesting that chronic sunlight exposure can have a protective effect.”
Another study found that “Sun exposure is associated with increased survival from melanoma.” However, the researchers note that its not known whether this effect is due to the sun’s benefits or the increased likelihood of early detection in sunny regions.
According to the Environmental Health Perspectives study mentioned earlier:
To maximize protection against cancer, Grant recommends raising 25(OH)D levels to between 40 and 60 ng/mL. Research such as that described in Holick’s August 2006 Journal of Clinical Investigation article indicates that simply keeping the serum level above 20 ng/mL could reduce the risk of cancer by as much as 30–50%.”
With that said, a lot of factors contribute to overall health, and this research doesn’t mean that getting adequate levels of sunlight or having optimal vitamin D levels alone will prevent or treat any form of cancer. Also, although experts disagree on whether low-risk people need dermatological screenings, I live in a very sunny area and choose to visit a dermatologist once a year for a checkup.
10. Supports Oral Health
Several studies have found that sunlight – specifically UVB light – may reduce the incidence of dental cavities. One in particular found that children who lived in a sunny areas of Oregon had fewer cavities than kids who lived in less sunny regions.
Also, according to Washington University, sunlight exposure may improve gum health.
11. Benefits of Sun Exposure During Pregnancy
By the fourth month of pregnancy, babies in the womb react to light by turning toward or away from it. That’s why I often uncovered my huge pregnant belly and shared the warm glow of the sun with my little ones. I’m sure they enjoyed the light, but I know they enjoyed the feel-good hormones that flooded my body.
Beyond that, there may be other benefits, such as:
Stronger Bones – According to researchers at the University of Bristol, mothers who received regular sunlight during their third trimester gave birth to babies with stronger, wider bones.
Reduced Asthma Risk – In two separate studies, women who lived in sunnier areas during their third trimester reduced their children’s likelihood of developing asthma.
Frequently Asked Questions
Below are some thoughts on some of the most frequently asked questions about sunlight that I’ve received over the years. The only thing I don’t cover is which sunscreens I use, so I’ll follow up with a list in another article.
Can’t we just get our vitamin D from supplements and food?
As I mentioned above, some of the benefits of sunlight don’t appear to be directly tied to vitamin D production. In studies like this one, researchers have said that although vitamin D deficiency is linked to several health conditions, giving vitamin D supplements in order to try to treat them often yields disappointing results.
However, many cultures have long prized foods rich in vitamins D, A and K, which work synergistically together. I do, too, which is why my family takes raw cod liver oil regularly. It contains naturally occurring vitamins A and D, unlike most fish oils which remove them during a filtering/deodorizing process and then add synthetic ones back in. Find out why I opt for whole-food sources instead of isolated D3 and other vitamins here.
Other good sources of vitamin D are egg yolks, liver, and fatty fish like salmon, herring and sardines. We also prioritize foods rich in vitamin K2, which is found in fermented foods and animal fats (cheese, butter, eggs, emu oil or emu oil capsules). If you have certain beneficial gut bacteria, it can also be synthesized in your digestive tract.
Does sunscreen impair vitamin D production?
“Sunscreen, therefore, in addition to preventing suntan and sunburn, also reduces Vitamin D production by 97.5% (Seaing and Leung 2010). While no use of sunscreen clearly has both long- and short-term consequences, overuse may contribute to both the rise in Vitamin D deficiency and the increase in asthma prevalence.”
How much sun exposure is best?
So how much sunlight is enough to get the benefits, and how much is too much?
“As for what constitutes ‘excessive’ UVR exposure, there is no one-size-fits-all answer,” says Robyn Lucas, who coauthored a World Health Organization report on UV light. She adds that “Excessive’ really means inappropriately high for your skin type under a particular level of ambient UVR.”
While general recommendations tend to hover around getting 10-30 minutes of midday exposure a few times a week, there are several factors that may also be helpful to consider:
Geographic Area & Season
The intensity of the sun (UV index) varies based on your geographical region and the time of year. People who live closer to the equator generally produce sufficient vitamin D levels in a shorter amount of time than those who live further away.
In general, people with more melanin (a type of skin pigment) need more time in the sun to produce adequate levels of vitamin D. That’s because melanin absorbs UV radiation in order to protect skin, so less UV makes it to the skin layer that is responsible for making vitamin D.
According to one study, for lighter-toned people “a half-hour in the summer sun in a bathing suit can initiate the release of 50,000 IU (1.25 mg) vitamin D into the circulation within 24 hours of exposure; this same amount of exposure yields 20,000–30,000 IU in tanned individuals and 8,000–10,000 IU in dark-skinned people.”
Frequency of Exposure
As mentioned earlier, outdoor workers have a decreased risk of melanoma compared with indoor workers, which suggests that regular sunlight exposure can have a protective effect.
However, according to Harvard Medical School, “Several studies have suggested that suddenly getting a lot of sun is more dangerous than steady exposure over time.”
Bottom line: Frequency matters, and smaller regular exposures are better than more intense infrequent exposures.
Some argue that the health benefits of UVB radiation seem to outweigh the adverse effects, and that the risks can be minimized by carefully managing UVR exposure (e.g., by avoiding sunburn), as well as by increasing one’s intake of dietary antioxidants and limiting dietary fat and caloric intake. Antioxidants including polyphenols, apigenin, curcumin, proanthocyanidins, resveratrol, and silymarin have shown promise in laboratory studies in protecting against UVR-induced skin cancer, perhaps through antimutagenic or immune-modulating mechanisms.” (1, emphasis mine)
We’ll talk more about antioxidants in another post soon, plus why some types of fat may be more problematic than others.
Because supplementation doesn’t seem to fully replace all the benefits of sunlight, my family makes regular sun exposure a priority. With that said, we are careful to avoid getting sunburned and focus on getting smaller amounts of sunlight frequently instead of large amounts every once in awhile.