A Bitter Pill: The Limitations of Vitamin D Supplementation and the Irreplaceable Benefits of Sun Exposure

By Dr Alexis Jazmyn. PHD

Vitamin D deficiency has long been associated with numerous chronic diseases and aging-related conditions including: 

• autoimmune conditions (MS, RA, type 1 diabetes, lupus, Hashimoto’s and others)

• IBS and IBD

• type 2 diabetes & insulin resistance

• obesity

• high blood pressure

• coronary and peripheral artery disease, stroke, and heart failure

• osteoporosis 

• neurodegeneration (Alzheimer’s, Parkinson’s)

• depression

• anxiety

• seasonal affective disorder

• asthma and COPD

• multiple cancer types (colon, breast, prostate, pancreatic, ovarian, melanoma)

• PCOS and infertility

• chronic kidney disease

and more. 

This associational data has been a huge driving force for the widespread enthusiasm around vitamin D supplementation as a panacea. Yet, accumulating evidence clearly indicates that vitamin D supplements alone may not deliver the desired health outcomes. Instead, vitamin D levels serve as an indicator of one’s sun exposure habits, which carry broader and deeper health benefits beyond vitamin D itself.

Limitations of Vitamin D Supplementation in Chronic Disease

1. Cardiovascular Disease and Cancer

The landmark VITAL study involving over 25,000 participants found that vitamin D supplementation (2,000 IU daily) did not significantly decrease the incidence of major cardiovascular events or invasive cancer compared to placebo (PMID: 31733345).

2. Cognitive Function

Research published in the Journal of Neurological Sciences showed no improvement in cognitive performance in mid-aged and older adults following four months of vitamin D supplementation, challenging the notion of its neuroprotective benefits (PMID: 30472553).

3. Diabetes and Glucose Metabolism

Studies have consistently demonstrated a lack of improvement in glucose metabolism and insulin sensitivity with vitamin D supplementation. One study specifically found no benefits in glycemic indices, blood pressure, or lipid profiles following vitamin D administration in individuals with impaired glucose tolerance (PMID: 24947792). A broader review of 35 trials involving over 43,000 participants similarly concluded no meaningful impact on diabetes-related outcomes (PMID: 25062463).

4. Irritable Bowel Syndrome (IBS)

Vitamin D supplementation also failed to alleviate symptoms or improve quality of life in individuals suffering from IBS, highlighting yet another limitation in its therapeutic application for chronic conditions (PMID: 34328539).

5. Insulin Sensitivity and Obesity

Research involving overweight or obese adults deficient in vitamin D revealed that even high-dose supplementation did not enhance insulin sensitivity or secretion, further undermining claims about its metabolic benefits (PMID: 28490514).

Vitamin D as a Biomarker, Not a Therapeutic Target

The consistent lack of clinical improvements from vitamin D supplementation suggests blood vitamin D levels may merely reflect the amount of time an individual spends outdoors, exposed to sunlight and the multitude of benefits that result from such behavior. Indeed, unlike the narrow spectrum effect of supplementing with vitamin D3, full spectrum sun exposure on the skin and the eyes offers numerous direct and indirect benefits for your health.

1. UVB-Induced Production of Vitamin D and Related Compounds

UVB radiation from sunlight stimulates the production of pre-vitamin D from 7-dehydrocholesterol in the skin. However, in addition to supporting vitamin D status, over a dozen other vitamin D-like molecules are made in the skin in response to UVB light (PMID 32441029). Optimized vitamin D status (>=60 ng/mL) is associated with positive health outcomes including reduction in infectious disease incidence and severity, cancer risks, and musculoskeletal pathologies.

2. UVB-Induced Production of Pro-opiomelanocortin (POMC)

Exposure to UVB radiation triggers the production of pro-opiomelanocortin (POMC) in the skin and also in the brain via ocular UVB light exposure. POMC is cleaved into several important peptides, including alpha-melanocyte stimulating hormone (α-MSH) and β-endorphin:

• β-endorphin improves mood, reduces pain perception, enhances immune function, and supports metabolism, with evidence showing that it can assist in reducing body fat and improving overall metabolic health. Beta-endorphin supports mood by increasing dopamine in the brain. This not only supports mental health and critical thinking, but also boosts overall feelings of satisfaction and wellbeing which, in turn, reduces the drive to engage in compulsive and addictive behaviors including abuse of drugs, alcohol, junk food, sex, and social media all of which are behaviors associated with a low dopamine state. If the body doesn’t receive the signals from the light environment and/or physical activity to stimulate dopamine, then your brain will seek out quick hits of dopamine from other sources despite the consequences.
  
  

• α-MSH induces melanin synthesis in the skin and other parts of the body like the brain (loss of melanin in the substantia nigra is a hallmark of late stage Parkinson’s). It also interacts with the hypothalamus in the brain to boost energy expenditure and reduce appetite. Thus, adequate production of α-MSH is critical for the achievement or maintenance of healthy body composition and metabolic health
  
  

3. Melanin’s Protective and Health-Promoting Roles

Melanin, synthesized in response to UV-stimulated POMC production, offers profound health benefits. Melanin is what is gives your skin color when you get a “tan” and is what gives individuals from different ethnic backgrounds different skin tones. Melanin possesses multiple important health benefits:

• Heavy Metal Chelation: Melanin binds toxic heavy metals, facilitating detoxification and reducing oxidative damage from these molecules. This is true across species. For example, city pigeons have much darker plumage than their countryside counterparts. This is because the city pigeons deposit melanin into their feathers to help chelate heavy metal pollutants from their environments out of their blood and tissues and into the feathers (PMID: 24671830)

• Radiation Protection: Melanin effectively absorbs and neutralizes various forms of radiation (including the non-native EMF radiofrequencies and even gamma radiation), providing critical cellular protection (PMID: 38758918).

• Antioxidant Capacity: As a potent antioxidant, melanin reduces oxidative stress, helping to prevent chronic disease and support mitochondrial function (PMID: 16613501).

Researcher Arturo Solis Herrera further proposes melanin may play a critical role in what he calls "human photosynthesis". He hypothesizes that melanin can capture and convert light energy and in doing so provide the system with a source of free energy to run metabolism and maintain overall health. This role of melanin has proven to be active in other organisms. Specifically, mushrooms were discovered growing at Chernobyl that appear black in color due to the dense melanin present in their fruiting bodies. The researchers discovered that these mushrooms use melanin to make free energy from the gamma radiation in the environment (PMID: 28256187).

The amount of sun exposure needed to optimize the body varies depending on how much melanin an individual has in their skin. Individuals with darker skin (i.e. more melanin) require longer time spent in sunlight because melanin acts like a sponge for light. In other words, the more melanin you have in your skin, the less UV light is available to catalyze the creation of vitamin D and POMC, and the less red light is available to reach into your deeper mitochondria. This is adaptive because dark skin evolved to harness consistently intense sunlight present in equatorial regions, while loss of melanin tracks with human migration to high latitudes.

4. UVA-Induced Nitric Oxide Production and Circadian Syncing

UVA radiation from sunlight releases nitric oxide (NO) stored in skin tissues. NO is a powerful vasodilator that lowers blood pressure, improves circulation and thereby supports nutrient and oxygen delivery to tissues and waste removal from tissues. Defects in NO are a major underlying causal factor in cardiovascular disease (PMID: 29388567). Because UVA stimulates the production of NO in the skin, followed by its diffusion into the circulation, the amount of NO produced is proportional to the amount of skin exposed to sunlight.

Additionally, neuropsin, a UVA light detecting protein, is ubiquitously expressed across the skin and eyes, as well as other tissues including the testes, hair follicles, retina, and brain. Neuropsin helps to synchronize circadian clocks within these tissues to the UV light availability in the environment. The presence, absence, and quantity of UV light in the environment informs the body about both the time of day AND time of year. Stimulation of neuropsin by UVA light has also been shown to support vitamin D and melanin production in the skin. It has also been shown to play a role in the production of hormones including melatonin and the sex steroid hormones like testosterone, estrogen, and progesterone (PMID: 34952723).

5. Red and Infrared (IR) Light and Mitochondrial Function

Exposure to red and IR wavelengths enhances mitochondrial efficiency, boosting cellular energy production and reducing inflammation. Through these mechanisms, these long wavelengths of light mitigate metabolic disorders, chronic fatigue, and slow cellular aging. Midday sun is over 50% red and IR light. Regardless of what time of day it is, if you are outside and it’s light out, you are being bathed in these healing frequencies. Modern indoor environments are highly deficient in these frequencies, especially near-infrared (NIR) light which is the type of light with the deepest penetrance. In other words, NIR light has the ability to penetrate through skin and bone to reach your deepest mitochondria.

Energy efficient lighting and device screens are completely devoid of both NIR and UV light, and standard window glass blocks almost all NIR and UVB light. Modern humans spend over 90% of their time indoors and when they do go outside, they are wearing sunglasses, contacts, prescription glasses, sunscreen, and ample clothing. In other words, the modern human is severely deficient in UV and NIR light, both of which play critical roles in achieving and maintaining health through supporting mitochondrial function, autophagy, and bioenergetics.

Sun Exposure and Reduction of Chronic Disease Risk

A growing body of research highlights a clear inverse relationship between regular sun exposure and the incidence of several chronic conditions (PMID: 28074966):

• Autoimmune Diseases: Increased sun exposure correlates with lower incidences of autoimmune diseases, including multiple sclerosis and rheumatoid arthritis, likely due to immunomodulatory effects of vitamin D, POMC peptides, and NO.

• Diabetes and Obesity: Sun exposure, independent of vitamin D levels, is linked to improved glucose metabolism and reduced obesity rates. Enhanced mitochondrial function and the metabolic effects of POMC peptides play crucial roles here.

• Cardiovascular Disease: Regular sunlight exposure has been consistently associated with improved cardiovascular health, likely driven by UVA-induced nitric oxide production and improved mitochondrial function from red and infrared wavelengths.

• Neurodegeneration: Emerging evidence suggests sunlight exposure offers protective effects against neurodegenerative diseases such as Alzheimer's, possibly through enhanced mitochondrial function, reduced inflammation, and neuroprotective peptides derived from POMC.

Given that low vitamin D is a risk factor for all of these conditions, and vitamin D supplementation has failed to show any meaningful benefits in these domains, the clear interpretation is that the chronic disease burden we are experiencing is directly related to modern man’s migration from outdoor living to indoor living, further exacerbated by the demonization of sun exposure by the centralized paradigm. 

Conclusion

Thus, rather than optimizing serum vitamin D levels through supplementation, the scientific evidence strongly supports promoting regular, daily sun exposure as a comprehensive strategy for preventing chronic disease and optimizing overall health. Vitamin D status is best viewed as an indicator of an individual’s sun exposure and time spent outdoors rather than as an isolated therapeutic goal. Recognizing the multifaceted benefits of sunlight beyond vitamin D has the potential to shift the paradigm from supplement-centric strategies toward nature-based, low cost solutions that everyone can access and from which all can receive meaningful benefits.

 

References

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