September 22nd marks the autumn equinox and, in the northern hemisphere at least,
heralds the gloomy six-month period during which the nights will be longer the days.
As a result, millions of sun-starved northern Europeans
will flee to the beaches of the Caribbean or north Africa in search of some winter rays.
Their doctors would probably rather they stayed home.
Besides ageing the skin prematurely, the ultraviolet (UV) radiation in sunlight also scrambles DNA.
That causes skin cancer, worldwide rates of which are rising steadily.
And although some sunlight is necessary to make vitamin D, this nutrient can also be obtained from food or pills.
For that reason, public-health advice over the past few decades has tended to emphasise avoiding the sun,
via seeking shade, covering up and using sun cream.
But perhaps that advice has gone a bit too far—at least for denizens of gloomy countries at high latitudes.
A growing body of research hints at health benefits from sunlight that go beyond just those offered by vitamin D.
These include protections against heart disease, cancer and autoimmune diseases.
A study published last year, for instance,
examined medical data from 360,000 light-skinned Brits and found that greater exposure to UV radiation —
either from living in Britain's sunnier southern bits rather than the darker north,
or from regularly using sunbeds—was correlated with either a 12% and 15% lower risk,
respectively, of dying, even when the raised risk of skin cancer was taken into account.
That fits with the results of another big study published a decade earlier.
Led by Pelle Lindqvist, an epidemiologist at the Karolinska Institute in Stockholm,