Pivoting from “harmful” to “healthy,” the public health rhetoric on sunlight and its healing properties has transformed in recent years, largely due to the benefits of vitamin D exposure.
For more than a century, public health messages focused on the adverse effects of sunlight on our health. Overexposure to sunlight is linked to negative consequences, such as skin-damaging sunburns, raising the risks for skin cancer, and even cataracts.
However, the public health narrative has now evolved due to the availability of new sunscreens, supplements, and light therapies, not to mention scientific findings highlighting the multiple health benefits associated with sunlight. Sunlight has been linked to boosting serotonin, helping improve mental health, building strong bones, contributing to cancer prevention, and healing skin conditions.
Studies also indicate preliminary evidence for sunlight as a potential treatment for rheumatoid arthritis (RA), systemic lupus erythematosus, inflammatory bowel disease (IBD), and thyroiditis.
Harm from the sun remains a crucial consideration, however. People can protect their skin from too much sun by applying sunscreen with at least a sun protective factor (SPF) 50, avoiding direct sunlight and subsequent sunburn, and wearing sun-protective clothing and UVR-filtered sunglasses.
Risks of Too Little Sun
A 2020 research study suggests that “insufficient sun exposure is a significant public health problem” and cited previous research linking it to an estimated 340,000 deaths in the US and 480,000 in Europe per year. Further, a lack of exposure to sunlight may increase the prevalence of various conditions, including breast and colorectal cancers, cardiovascular disease, multiple sclerosis, Alzheimer’s disease, autism, and asthma.
A 2020 research study suggests that “insufficient sun exposure is a significant public health problem.”
Exposure to the sun’s rays causes the skin to produce vitamin D, which has long been considered the primary benefit of sunlight. The sun’s rays contain ultraviolet-B radiation, which makes the vitamin.
“Vitamin D plays a critical role in immune function,” Dr. Michael Holick, professor of pharmacology, physiology, biophysics and molecular medicine, and director of the Ehlers-Danlos Clinical Research Programme at Boston University School of Medicine, told The Earth & I.
Calls to rethink sun exposure policy or to promote vitamin D supplementation in higher-risk populations were prominent fifteen years ago, with one particular study highlighting this need. However, since then, results indicate that while likely to be more beneficial than not, researchers have not convincingly shown that vitamin D oral supplementation helps to prevent these conditions.
In a 2022 webinar, Dr. Roger Seheult, an associate professor at the University of California Riverside School of Medicine, spoke on several topics, such as sunlight's positive role on cell health by interacting with melatonin, humans’ widespread deficiency in sunlight exposure, and its overall health impact.
Sunlight and the Covid-19 Pandemic
In February 2022, Dr. Holick published an editorial paper in the journal Nutrients on the prominence of vitamin D deficiency in the COVID-19 era. The paper, entitled The CO-VID D-Lemma: A Call for Action, cited previous research suggesting that people with ample amounts of vitamin D had lower risks for respiratory infections and clinical complications, such as those connected to COVID-19.
The COVID-19 pandemic reduced sunlight exposure due to widespread stay-at-home policies, resulting in difficulty in “active and healthy aging,” 2021 research found. The review study also found that phototherapy with full-spectrum light is a potential alternative to sunlight exposure.
The researchers recommended future studies focus on screening optimal phototherapy conditions, such as light strength, effective wavelength, and exposure duration.
Through previous findings, researchers knew that activated macrophages produce 1,25-dihydroxy vitamin D, which interacts with both T and B lymphocyte cells. These cells are responsible for making antibodies and cytokines.
Scientists also know that during COVID-19, one of the significant complications of infection was the cytokine storm. “So, vitamin D, playing a critical role in both adaptive and innate immunity, would reduce the risk of developing infection, morbidity and mortality,” Dr. Holick adds.
During COVID-19, one of the significant complications of infection was the cytokine storm. “So, vitamin D, playing a critical role in both adaptive and innate immunity, would reduce the risk of developing infection, morbidity and mortality.”
Researchers conducted various studies to prove this. The first published study Dr. Holick undertook evaluated 191,000 COVID-19-positive patients throughout the US for their vitamin D status. They found that patients with a circulating concentration of 25 hydroxy vitamin D of at least 34 nanograms per ml had a 54% reduced risk of COVID infection. Another study showed that if COVID-19 patients went into a hospital with adequate vitamin D status, they had less risk for complications or death.
Mirroring the recommendation over a century ago during the Spanish flu pandemic, researchers advised sensible sun exposure during the COVID-19 pandemic and a healthy vitamin D status with dietary and supplemental vitamin D. Today, as the world population edges away from the COVID-19 pandemic, vitamin D sufficiency is no less critical, as it offers multiple health benefits that are difficult to replicate artificially.
Is Vitamin D All About the Sun?
“Herein lies the problem,” Dr. Holick responds when asked if vitamin D is solely associated with sunlight or if other factors are present. “It’s well-recognized that vitamin D deficiency is probably the most common medical condition worldwide—at least a billion people in the world are vitamin deficient,” Dr. Holick adds.
The reason is simple, however. Research indicates that people living in Calgary, Canada, or the UK, or at similar northern latitudes cannot make any vitamin D in their skin for six months, from approximately October until mid-April.
People naturally turn to other vitamin D sources, though these are limited as there are very few dietary sources. “Oily fish, and mushrooms exposed to sunlight, and cod liver oil are your only dietary sources of vitamin D,” says Dr. Holick. Wild-caught salmon contains 500 to 1,000 units in a serving, while farmed salmon has only about 10% to 20% of that amount.
In addition, the public has been taught to avoid the sun by going outside only in early mornings and late afternoons. That kind of schedule largely defeats the idea of getting vitamin D. “It turns out you make none” at those times, says Dr. Holick, adding that people only make vitamin D from about 10:00 a.m. until 2:00 p.m., regardless of whether one lives at the equator, in Panama, or in Boston.
Circadian Rhythms and the Sun
Circadian rhythm refers to human physical, mental, and behavioral changes in a 24-hour cycle. Astronauts’ cycles increase by over an hour because they no longer have the typical circadian rhythms humans are born with. Alertness in the morning is due to the adrenal corticotropin hormone from the pituitary gland, which wakes people up. It sends a signal to the adrenal glands to make cortisol so that cortisol levels at 7:00 a.m. to 8:00 a.m. are high and robust to help people wake up.
“There has been an evolution in our thinking about sun exposure,” says Dr. Holick. After recognizing that the time of day, season, and latitude create skin pigmentation, all of which influence the ability to make vitamin D, Dr. Holick developed an app called dminder.
The app is designed to tell the user when they can begin making vitamin D and how much is made, and it warns them to get out of the sun so they do not get sunburned. The app cannot customize the results based on each person’s condition; however, it does consider health factors that can affect vitamin D, such as skin type, obesity, or a granuloma disorder.
Bright Light Therapy: A Solution for Autumn and Winter?
Without access to sunlight and with the prominence of SAD, vitamin D sources are limited, prompting potential deficiency. Vitamin D supplementation is advised throughout the year to support sufficiency. “I recommend that everyone take the supplement every day, spring, summer, fall, and winter, because your blood level excursion [fluctuation] of vitamin D is very little,” says Dr. Holick.
Without access to sunlight …, vitamin D sources are limited, prompting potential deficiency. Vitamin D supplementation is advised throughout the year to support sufficiency.
Artificial sources can also provide a solution, particularly in autumn and winter. “Bright light therapy is the most effective way of helping people with seasonal affective disorder,” says Dr. Holick. The recommendation is to use at least a lamp with 10,000 LuxS. Turning the indirect light on in the morning while preparing breakfast or reading a newspaper helps suppress melatonin.
Technology developers are creating artificial sources of red light designed to provide some of the beneficial infrared wavelengths of the sun’s light without going outside. Companies such as Mito Red Light produce light therapy products to help people access artificial sunlight.
Presenting their “tentative evidence,” researchers in a 2020 study on sunlight and health showed that red and near-infrared light, both present in sunlight, could explain the associations between sunlight exposure and better health status.
*Natasha Spencer-Jolliffe is a freelance journalist and editor. Over the past 10 years, Natasha has reported for a host of publications, exploring the wider world and industries from environmental, scientific, business, legal, and sociological perspectives. Natasha has also been interviewed as an insight provider for research institutes and conferences.
Source: Interview with Dr. Michael Holick, Professor of pharmacology, physiology, biophysics and molecular medicine, and director of the Ehlers-Danlos Clinical Research Program at Boston University School of Medicine.