Health Agencies Hid Sunlight’s Perks?

Crowded beach with people sunbathing and playing in the water

A science journalist’s new book argues that decades of “avoid the sun” advice may have quietly harmed millions of Americans — and the evidence backing that claim is harder to dismiss than you might expect.

Quick Take

Journalist Rowan Jacobsen’s 2026 book In Defense of Sunlight argues that moderate sun exposure supports hormones, mood, blood pressure, and immune health — not just vitamin D.
Emerging research links ultraviolet light to lower rates of several autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, and Crohn’s disease.
Sunlight triggers biological responses — including nitric oxide release and endorphin production — that supplements cannot fully replicate.
The real debate is not sun versus no sun, but how much is enough — and whether public health messaging has gone too far in one direction.

The “Zero Sun” Policy Under the Microscope

For decades, the standard advice has been simple: cover up, wear sunscreen, stay out of the sun. Skin cancer is real, and the warning made sense. But science writer Rowan Jacobsen spent years digging into what that advice may have cost us. His conclusion, laid out in In Defense of Sunlight, is that sunlight acts as a “master regulator” of human biology — shaping hormones, mood, sleep, and blood pressure in ways that no pill fully replaces.^[1]

Jacobsen is not telling people to bake in the sun all day. His argument is more careful than that. He says a “zero sun” default has real health costs, and that a little direct exposure — even ten minutes outside with skin uncovered — may do more good than harm for most people.^[3] That nuance often gets lost when institutions default to the simplest safety message.

What Sunlight Actually Does to Your Body

Sunlight does more than make vitamin D. When ultraviolet light hits skin, cells release nitric oxide, which relaxes blood vessels and lowers blood pressure. Skin cells also produce a molecule called pro-opiomelanocortin, which the body breaks into beta-endorphins and other compounds tied to mood and pain relief.^[4] These are not small side effects — they are direct biological responses that happen within minutes of sun exposure and cannot be replicated by taking a supplement.

The vitamin D story alone is worth revisiting. Sunlight on skin produces vitamin D naturally, which helps move calcium into bones.^[3] Vitamin D supplements have been widely studied, but trial results have been disappointing. Jacobsen argues that the full package of benefits from real sunlight goes far beyond what a capsule can deliver — a point that dermatology guidelines have been slow to absorb.^[2]

Sunlight and Autoimmune Disease: A Growing Body of Evidence

One of the more striking areas of research involves autoimmune diseases. Conditions like multiple sclerosis, type 1 diabetes, rheumatoid arthritis, Crohn’s disease, and colitis are all more common in people who get very little sun. Ultraviolet light appears to calm overactive immune responses — the kind that cause these diseases in the first place.^[4] Researchers believe this happens through pathways separate from vitamin D, which is why the supplement alone has not solved the problem.

This is not fringe science. Scientific American covered the autoimmune angle in depth, noting that the mechanism involves direct immune suppression through ultraviolet exposure.^[4] Jacobsen’s book pulls together this evidence and asks a fair question: if sun avoidance increases the risk of serious chronic illness, why is that cost almost never mentioned in public health messaging? The institutions that set those guidelines tend to focus on a single risk — skin cancer — without weighing the full picture.

A Familiar Pattern: One Risk, Hidden Costs

This debate follows a pattern that shows up repeatedly in medicine and public policy. An institution identifies a real danger, builds messaging around it, and the message hardens into dogma. Over time, the hidden costs of the policy pile up — but they are harder to see because they are spread across millions of people and dozens of conditions. Jacobsen published a piece in The Atlantic in 2024 asking why American experts would not acknowledge that moderate sun exposure can be good for you.^[17]

Sunlight might be one of the most misunderstood parts of modern health. ☀️ In In Defense of Sunlight, Rowan Jacobsen explores the science behind Vitamin D, wellness, and why we may need more time outside—not less.

On sale 6/16/26: https://t.co/2M4so3w92L pic.twitter.com/lOj5X85UbQ

— Scribner (@ScribnerBooks) June 13, 2026

The honest answer is that “some sun is fine, just don’t overdo it” is a harder message to deliver than “stay out of the sun.” Nuance is hard to put on a pamphlet. But when the simplified version of the advice steers people toward chronic sun avoidance, the biological costs are real. Jacobsen is not anti-dermatology. He is asking for a more honest accounting — one that weighs both sides of the equation rather than treating any sun exposure as inherently dangerous.^[9] That is a reasonable ask, and the science increasingly supports it.