On the Bookshelf: In 'The Sunlight Solution,' William Supple Argues More Time in the Sun Can Help Americans Heal

A review of 'The Sunlight Solution,' a new book by William F. Supple Jr., due out from MAHA Books on June 23, 2026

“The return on investment of a sensible sun and vitamin D public health policy could be among the most profound in human history.”

— William F. Supple Jr., PhD

How many times did a parent or teacher tell you to be careful of the sun, wear a hat, apply sunscreen, and so on?

But what if all these well-meaning people were wrong? What if the sun is really our friend and is good for us?

That is part of the argument put forward by William F. Supple Jr., a Dartmouth-trained neuroscientist specializing in systems neurobiology, learning, and memory. In his new book, The Sunlight Solution (MAHA Books/Skyhorse Publishing, June 23, 2026), Supple says that the systematic campaign to remove sunlight from American life is making us vitamin D deficient and thereby driving epidemic levels of chronic disease.

Citing hundreds of peer-reviewed studies, Supple walks readers through the major physiological systems affected by vitamin D deficiency, from cardiovascular health and immune function to brain development and metabolic disease.

Nearly 80% of Americans now have at least one chronic disease, with 51.4% reporting multiple chronic conditions. This is up from 11% in the 1960s, according to the CDC, and is also the epidemic MAHA was created to reverse. Supple argues that if we fix vitamin D deficiency we take a major step toward helping Americans heal.

To understand why fixing vitamin D is so important, it’s equally important to note that it’s not really a vitamin at all. It is a master hormone, with receptors on virtually every cell in the body. That fact reframes everything that follows, starting with the cancer that the sun-avoidance campaign was created to prevent.

The Melanoma Paradox

Melanoma is the deadliest form of skin cancer, and for 50 years it has been the justification for the sun avoidance recommendation. But the data tells a stranger story, as Supple lays out with detailed evidence in Chapter 25. Melanoma frequently occurs on areas of the body that get little to no sun exposure, including the soles of the feet, palms, under fingernails, mucosal membranes and the groin.

People who work outside and get chronic sun exposure tend to have lower melanoma risk than indoor workers who get occasional intense exposure. Most striking, a Swedish study of 30,000 women found that avoiding the sun carries an all-cause mortality risk comparable to smoking.

Vitamin D deficiency is now linked to worse melanoma survival, meaning decades of sun-avoidance advice may have made the very cancer it was designed to prevent more deadly.

Is Sunscreen the New Margarine?

Americans started replacing butter with margarine to prevent heart disease, only to discover that trans fats were more dangerous than the butter. The same pattern is unfolding with sunscreen. The FDA’s own funded studies confirmed that oxybenzone, octinoxate, and other common sunscreen chemicals are absorbed systemically after a single application, reaching plasma concentrations more than 500 times the FDA’s safety threshold within days. And the damage from sun avoidance is not just skin deep; its far-reaching effects go to the bones and muscles as well.

Sunlight and Muscle

Skeletal muscle cells contain vitamin D receptors, and muscles that contain type II fast-twitch fibers have the highest concentration of vitamin D receptors. These muscle fibers dominate quick movements, like catching yourself before a fall. When vitamin D levels fall, these fibers shrink, setting off a preventable cascade of weakness, pain, inactivity, atrophy, fracture, hospitalization, and, in elderly patients, often death. Hip fractures in the elderly carry a one-year mortality rate of roughly 20 to 30% due to complications.

Vitamin D also inhibits myostatin, the body’s natural brake on muscle growth, so a deficiency suppresses muscle growth and strength, even when actively lifting weights. In the muscle chapter of The Sunlight Solution Supple writes that sarcopenia, the age-related loss of muscle, is not a disease of aging – instead, it’s a disease of chronic vitamin D starvation. That same deficiency that weakens muscles can also weaken the brain.

Immunity, the Brain, and the Autism Connection

Vitamin D is among the most potent modulators of immune-driven inflammation, which is the common mechanism underlying cardiovascular disease, cancer, neurodegeneration, and autoimmunity. Supple documents a decline in NIH funding for vitamin D research, finding a drop from $52.4 million to $10.5 million in 2024, even as evidence of its systemic significance has grown.

Then there is the autism question. Robert F. Kennedy Jr. has made this a central mission at HHS, and Supple’s evidence points squarely to one factor that has gone largely ignored. A recent study found that only 1.36% of pregnant women have sufficient vitamin D levels. Supple presents evidence that chronic maternal vitamin D deficiency creates a neuroinflammatory vulnerability in the developing brain, one that is then worsened by the neurotoxic exposures including sunscreen chemicals.

Supple extends his vitamin D argument into microplastics. In a recent Substack essay, he argues that microplastics may contribute to chronic inflammation in tissues, while vitamin D helps regulate the immune response that determines how much damage that inflammatory burden causes.

The science is still emerging, but the point fits the theme of The Sunlight Solution. In a world filled with modern environmental stressors, restoring vitamin D sufficiency may be one of the simplest ways to strengthen the body’s natural defenses.

For the MAHA movement, which is working to identify environmental and biological insults that may contribute to the autism epidemic, a population-wide hormone deficiency in pregnant women is a point that cannot be ignored. And the neuroinflammation appears to be reversible in children who have already been diagnosed. A clinical trial published in BMC Pediatrics found that after 15 weeks of vitamin D supplementation, children with ASD showed significant drops in inflammatory markers and meaningful improvement in behavioral symptoms.

This is just one of the many significant findings in Supple’s essential book. As the author helps me consider: There are real reasons a patch of sunlight feels so therapeutic, why we turn our faces toward it the way plants lean toward a window. We are built to seek the sun, and being told to fear it runs against something very primal in us. We are not meant to live in the shadows. We need the sun the way we need food, water, and sleep, along with the vitamin D that only it can fully give us.

Supple makes his case eloquently and with deeply researched science, showing how a single beam of light improves our physical and mental health, our resilience, and even the length of our lives. Sunlight is not a luxury or a hazard to be managed. It is a basic biological need, as old as life itself, and we should not let big medicine talk us out of the very thing we have always, instinctively, reached for.

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The Sunlight Solution: Reclaiming Vitamin D, Reversing the Chronic Disease Epidemic, and Making America Healthy Again, by William F. Supple Jr., is scheduled for release by MAHA Books, an imprint of Skyhorse Publishing, on June 23 and is available for pre-order here.

The Sunlight Solution: Reclaiming Vitamin D, Reversing the Chronic Disease Epidemic, and Making America Healthy Again, by William F. Supple Jr., is scheduled for release by MAHA Books, an imprint of Skyhorse Publishing, on June 23 and is available for pre-order here.