Living in Vermont, science and nature writer Rowan Jacobsen noticed the effects the seasons had on him. Summers were gorgeous, but the grey winters were brutal and left him lagging.

“I felt as if my cells didn’t work,” he writes in his new book, “In Defense of Sunlight, The Surprising Science of Sun Exposure” (Scribner).

But, during sunnier times, when he got some early morning rays, he writes “It was as if some nutrient was pouring from the sky.”

While the sun and its UV rays have been vilified in recent decades, Jacobsen offers up a counter narrative.

“The science consistently showed that people who received ample amounts of sun exposure lived longer, healthier lives than people who didn’t,” he writes.

He said his “wake-up call” came after reading a “paradigm-shifting” 2018 report in The Journal of Cell Science.

Chinese neurology researchers found that those who had sun exposure were healthier and lived longer, even when they suffered from diabetes or heart attacks.

“Like most people, I’d had it drilled into me …that the sun was bad news, the primary cause of skin cancer” and that the only acceptable sunlight on unprotected skin was “zero,” Jacobsen writes.

He notes that the suncare business is booming, worth an estimated $15 billion, largely thanks to heavily promoting protection against sunburn and possibly skin cancer. But skin cancer rates haven’t gone down as sunscreen sales have risen.

“The European Journal of Dermatology published a meta-analysis of the 29 studies of sunscreen use and skin cancer that had been done since the 1970s,” he writes. “All of them showed a higher risk of skin cancer among the sunscreen users.”

In 1979, intense lobbying by the industry convinced the Food and Drug Administration to allow cosmetics companies to claim that the use of sunscreen might help reduce the risk of skin cancer. Sales skyrocketed, but so have skin cancer rates.

Jacobsen believes that safe exposure to the sun’s rays can actually lower blood pressure, and build a healthier immune system. Meanwhile, he writes that some sunscreen products contain a high concentration of potentially harmful chemicals.

“In 2008, the Center for Disease Control (CDC) published a study showing that 97% of Americans were contaminated with oxybenzone, the most common and concerning of the sunscreen chemicals. It turns out oxybenzone and other related chemical filters penetrate the skin,” writes Jacobsen.

He also asserts that many suncare product contain phthalates and PFAS, “two extremely worrisome classes of chemicals that easily migrate into the body.” Phthalates have been connected to neurological disorders, reproductive abnormalities, and metabolic dysfunction.

Some four decades ago, the FDA introduced the Sun Protection Factor (SPF) system, which measures how much a sunscreen product can protect skin from ultraviolet rays — the sun’s burning rays. Sales of skin care products using the system soared.

But Jacobsen asserts that “SPF transformed a [sunscreen] that had all the gravitas of surfboard wax into an anchor of wellness with endless options in strength, formulation and price.”

He cites a study in 2014 by a team of dermatologists at Harvard Medical School that showed that the sun had profound mood-boosting powers.

It found that when exposed to the sun, skin cells produce a large molecule called proopiomelanocortin (POMC) that splits into three compounds.

One compound is responsible for triggering melanin, the pigment that protects from burning and tans skin. The second compound produces cortisol, which makes cells fire faster, making you feel more alert, more focused and able to burn more energy. The third compound infuses the brain with natural opioids — producing a “state of bliss similar to the effects of opium or morphine,” writes Jacobsen.

Another questionable development in the booming skincare business, notes the author, was the aggressive marketing of Vitamin D supplements that were promoted as the new “wonder drug,” promising to increase the level of D in people who it was claimed weren’t getting it from the sun.

The supplement industry “quickly cranked out D pills by the billions,” writes the author. Even cancer foundations got in to promoting it.

Sales soared, but, in 2022, the New England Journal of Medicine reported in 2022 that Vitamin D supplements provided “zero benefits for any condition.”

Still, Jacobsen told The Post, “Vitamin D remains one of the most prescribed supplements in the world, even though it has been shown not to improve any health condition in those who have adequate levels of D already…It’s not a functional replacement for sun exposure.”

He advises that the best medicine is “right outside the door” – the sun itself.

“You should make sure to get at least a few minutes per day of sun exposure,” he said. “Those with darker skin should get a bit more, as should those living in darker places, or darker times of the year.”

He doesn’t advise ditching sunscreen altogether, but advocated wearing it only when needed and avoiding anything higher than 30 SPF. Don’t get burned and use common sense, but also don’t stay inside all the time or constantly cover up.

He said, “Get sun. Not too much. Go outside.”