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Sunlight Improves Gut Health

Analysis by Dr. Joseph Mercola Fact Checked

benefits of sun exposure

Story at-a-glance -

  • Recent data show that the fat-soluble hormone known as vitamin D modulates your gut microbiome, creating a healthier environment. This is likely one of the reasons sunlight has a positive effect on those suffering from inflammatory bowel disease and multiple sclerosis
  • Vitamin D is known as the sunshine vitamin because it's manufactured by the skin after exposure to UVB from the sun; insufficiency is associated with heart disease, lupus and stroke and may exacerbate chronic gut inflammatory diseases
  • RNA sequencing of stool samples from before and after the study intervention showed UVB light altered and improved the gut microbiome in women whose vitamin D levels were low, but didn't have an impact on those whose levels were higher
  • The combination of overusing antibiotics and getting low sunlight exposure may be driving societal alterations in the gut microbiome, leading to inflammatory diseases. Your best first option is sensible sun exposure, followed by phototherapy devices and then vitamin D supplementation

Although vitamin D is technically not a vitamin, it is crucial to several important processes in your body. The chemical is a fat-soluble hormone your body makes when your skin is exposed to sunlight. It’s not commonly found in whole food, but is added to some processed foods. It’s also available in supplement form.

Since your skin manufactures vitamin D when it's exposed to certain wavelengths of light found in phototherapy devices and sunlight, it's known as the sunshine vitamin. In the past years, researchers revealed the important role vitamin D plays in modulating cell growth, optimizing your neuromuscular and immune functions and helping your gut absorb calcium.

Chronic deficiency in vitamin D is associated with bone diseases, such as rickets and skeletal deformities. However, you don't need an outright deficiency to experience the negative effects of low levels of vitamin D. Insufficiency is also related to several health conditions, including accelerated aging, high blood pressure, behavioral problems in adolescents and elevated leptin levels, which can lead to obesity.

UVB Exposure, Gut Health and Inflammation

A research team1 from the University of British Columbia was interested in determining whether exposure to UVB light would have an effect on the human gut microbiome. The results of recent studies have suggested vitamin D could alter it, while the authors of past studies have shown UVB exposure triggers gut microbiome changes in rodents.2

There are few natural foods with vitamin D, so 80% of your body's requirement is typically met through skin exposure to UVB light. Those who live farther north or south of the equator, spend hours indoors or choose to stay away from sunlight have a higher risk of vitamin D insufficiency.3

Exposure to sunlight has a positive effect on those suffering from inflammatory bowel disease (IBD) and multiple sclerosis (MS); both diseases are exacerbated by inflammation. The researchers from British Columbia expounded on this, writing:4

“Our observations support findings that humans display seasonal fluctuations in their microbiome composition, potentially coinciding with fluctuations in serum vitamin D levels throughout the year.”

And:

“Several chronic inflammatory diseases display seasonal patterns in the severity of disease. Specifically, the relapsing and remitting nature of IBD and MS are strongly associated with vitamin D levels.

Exacerbations in IBD activity are commonly reported when serum vitamin D levels are low, with our data raising the question of whether these changes in disease activity could be precipitated by concurrent changes in microbiome composition.”

Sun Exposure Results in Greater Gut Diversity and Health

Since insufficient sunlight exposure may exacerbate or trigger chronic gut inflammatory diseases and vitamin D has an impact on gut microbiome diversity, the team designed a study to look at the influence these factors may have on each other. They enrolled 21 healthy young women who had been living in Canada for the entire winter and likely had not had enough sunlight exposure.

Before the start of treatment with narrow band UVB light (NB-UVB), the researchers took stool samples to analyze gut bacteria diversity. They also took blood samples to determine vitamin D levels.5 Over the course of one week the female volunteers underwent three one-minute sessions of full body NB-UVB light exposure.

NB-UVB light has demonstrated effectiveness in the treatment of skin disorders.6 Twelve of the 21 subjects were not taking vitamin D supplements and demonstrated a less diverse gut profile than those who regularly did so.7

RNA sequencing was used on the fecal samples taken before and after the intervention.8 The results revealed the short exposure to NB-UVB light increased vitamin D levels and altered gut microbiome. The women with initially low levels of vitamin D also had a lack of diversity in their gut microbiome.

After the intervention, there was an increase in the number of species, particularly Lachnospiraceae, which is associated with good health. Researcher Bruce A. Vallance, Ph.D., from British Columbia Children’s Hospital, was excited by the results of the study, commenting:9

“Prior to UVB exposure, these women had a less diverse and balanced gut microbiome than those taking regular vitamin D supplements. UVB exposure boosted the richness and evenness of their microbiome to levels indistinguishable from the supplemented group, whose microbiome was not significantly changed.”

And he pointed out:10

“In this study, we show exciting new data that UVB light is able to modulate the composition of the gut microbiome in humans, putatively through the synthesis of vitamin D. It is likely that exposure to UVB light somehow alters the immune system in the skin initially, then more systemically, which in turn affects how favorable the intestinal environment is for the different bacteria.

The results of this study have implications for people who are undergoing UVB phototherapy, and identifies a novel skin-gut axis that may contribute to the protective role of UVB light exposure in inflammatory diseases like MS and IBD.”

Cost of Rising Number of Immune and Inflammatory Diseases

The results of this study have the potential to affect a large population of those suffering from immune mediated or inflammatory diseases that may respond to changes in the gut microbiome. The numbers and range of those suffering are on the rise in Western society, due in large part to changes in how we live and the environments in which we live.11

The combination of antibiotic overuse and low sunlight exposure have likely driven changes to the composition of the gut microbiome, which in turn is linked by scientific evidence to chronic inflammatory conditions. Inflammation is part of the immune system's response and is one way of signaling the start of healing and the repairing of damaged tissue.

However, ongoing inflammation response is associated with heart disease, stroke, lupus and arthritis.12 The price tag to communities and families from the rising number of these diseases encompasses financial, mental and emotional burdens.

The results from this study demonstrate how sun avoidance and vitamin D insufficiency may well be major underlying and primary causes for the rising number of those who suffer premature morbidity and mortality.

Phototherapy Naturally Balances Your Vitamin D Levels

The research team believes the lack of sunlight is a driving force in the rising number suffering from diseases, writing:13 “Limited UVB exposure is one of the most important environmental factors linked to the onset of immune mediated chronic inflammatory diseases, like IBD and MS.”

While phototherapy devices, also known as tanning beds, are not advisable for tanning your skin, the researchers were able to attain good results with as little as three one-minute sessions in one week. There is a long history of using light for prevention and treatment, as you’ll discover in my article, “How Therapeutic Use of Full-Spectrum Light Can Improve Your Health.”

In addition to the development of vitamin D production, exposure to the sun in measured timeframes has a number of other health benefits Sun exposure can induce nitric oxide production, help relieve fibromyalgia pain, enhance your mood and energy and regulate melatonin. According to one study, nearly 70% of Americans suffer from insufficient vitamin D levels; the elderly with insufficient levels of vitamin D have an increased risk of death.

If you are unable to get sufficient amounts of regular sun exposure — the best way to raise your vitamin D level — supplements may help, although they are not a replacement for natural sunlight.

Why Vitamin D Supplements Cannot Fully Replace the Sun

As mentioned, sensible sun exposure is the best way to get vitamin D. If sun exposure isn’t feasible, oral supplementation is your next strategy. However, it's important to start by testing your vitamin D level and get as much sun exposure as you can to enjoy the additional benefits of UVB exposure.

GrassrootsHealth offers a helpful chart showing the average adult dose required to reach healthy vitamin D levels based on your tested starting point. While some experts believe you could take the supplement daily, weekly or monthly, I recommend a daily dose. This way, if you miss a day or two, it's not quite as bad as missing an entire week.

It's important to remember if you're taking vitamin D supplements, you also need vitamin K2. Vitamin K2 plays a crucial role in moving calcium from your blood into areas where it’s needed, such as your bones and teeth. It also helps remove calcium from areas where it shouldn't be, such as in your arteries and soft tissues.

Vitamin K2 deficiency is what produces the symptoms of vitamin D toxicity, which may include calcification leading to hardening of your arteries. As you take vitamin D, your body creates more vitamin K2-dependent proteins to move calcium around in your body. Without vitamin K2, these proteins are not activated and so the benefits are not realized.

So remember, if you take supplemental vitamin D, you're creating an increased demand for K2. Together, these two nutrients help strengthen your bones and improve your heart health.