Rowan Jacobsen opens his excerpt with a single, blunt line: "Basically, winter sucked." He follows that with a string of seasonal observations from his home in Vermont — feeling sharper in summer, eating less but doing more, and noticing that "My skin felt snappier, especially once it got a little color."
Spring of 2025 Fascination
Spring of 2025 is when Jacobsen says that fascination intensified and became the subject of a book project: he turned years of observing his own seasonal swings into In Defense of Sunlight: The Surprising Science of Sun Exposure. Jacobsen frames the pivot as cumulative — a pattern he noticed over the last seven years that finally crystallized in that spring — and he uses vivid contrast to explain why: a bright spring day after a long cloudy spell felt like a deep physical refill.
Rowan Jacobsen in Vermont
A team of details from Jacobsen’s Vermont life drives the excerpt: he cross-country skis "every decent day of winter" and, he concedes, "I probably get more focused cardio workouts in the snowy months." Yet he says his brain and body never felt fully online in winter — "I didn’t feel depressed in winter. I felt as if my cells didn’t work." At the same time, Jacobsen reports that most people he knew lost sharpness in winter and that many of them got depressed, which sets up the central contradiction of his account.
Harvard Medical School 2014 Finding
A team of dermatologists at Harvard Medical School confirmed the sun’s mood-boosting powers in 2014, and Jacobsen pulls that medical strand into his narrative to explain mechanisms. Skin cells produce a range of hormones when exposed to sunlight; one hormone triggered by sunlight produces melanin, the dark pigment that makes people tan and protects them from burning, and melanin also acts as a powerful antioxidant that can mop up damage caused by the sun’s rays. Sunlight also initiates the production of cortisol — described by Jacobsen with the phrase "in the zone" — and cortisol, the text says, is the hormone of activity: it makes cells fire faster, makes people more alert, makes people burn more energy, and makes people feel more focused.
The excerpt links these biochemical notes to concrete shifts Jacobsen lived through: feeling "way happier in summer," finding small things deeply pleasing, noticing a late-winter puffiness and a hint of a pouch in the mirror, and a blood pressure that would creep up "a few points" by late winter. Those are the operational, day-to-day signals he uses to justify turning personal habit into a research question.
In Defense of Sunlight: The Surprising Science of Sun Exposure is scheduled for release on June 16 from Simon & Schuster, and Jacobsen’s excerpt establishes the most urgent outstanding issue plainly: what specific evidence in the full book substantiates the claim that sunlight delivers measurable gains in mood, energy, and cognitive sharpness?
