For generations, Indians have been told: “Get some sunlight for vitamin D.” That advice is only partly about vitamin D. Natural daylight is one of the most powerful environmental signals for our circadian clock.
Regular exposure to bright outdoor light during the day can help regulate sleep–wake rhythms, alertness and mood. Spending time outdoors also encourages physical activity and reduces sedentary behaviour.
But sunlight is not a medicine where “more is better”. Its benefits and risks depend on time of day, latitude, season, skin pigmentation, clothing, air pollution and the amount of UV exposure.
There are two different reasons to step outdoors.
Morning daylight: Primarily for your biological clock
Bright outdoor light soon after waking provides a strong signal to the brain’s circadian system. This helps synchronise the sleep–wake cycle and may improve daytime alertness and nighttime sleep.
Importantly, you don’t need to stare at the sun, and you should never do so. Simply being outdoors in bright daylight is sufficient. Even on a cloudy day, outdoor light is usually far brighter than indoor lighting.
A practical target is 20–30 minutes outdoors in the morning, preferably as part of a walk or other activity.
The exact clock time matters less than the principle: get bright daylight early in your biological day. Your actual local sunrise, season and routine should determine the timing rather than a fixed 6:30–8:30 AM window.
Evidence that morning sunlight directly improves blood pressure through nitric oxide release is considerably less established than its role in circadian regulation, so it should not be presented as a treatment for hypertension.
Around midday: Primarily for vitamin D
Vitamin D production in the skin requires UVB radiation. UVB is much stronger when the sun is relatively high in the sky, which is why early-morning and late-afternoon sunlight may provide plenty of visible light but relatively little vitamin-D-producing UVB.
There is, however, no universal ‘15–20 minute’ prescription. The amount of UVB reaching your skin varies enormously with latitude, season, time of day, cloud cover, pollution, clothing and skin pigmentation.
Therefore, a fixed exposure time that works in Chennai may not work in Delhi in January.
In India, the southern states generally receive more favourable UVB conditions through the year. In northern India, winter, particularly with fog and air pollution, can substantially reduce UVB availability.
Darker skin also requires more UV exposure to produce the same amount of vitamin D because melanin reduces UVB penetration.
The practical message is simple: Aim for short, regular outdoor exposure without getting sunburned. Do not deliberately remain in strong midday sun for prolonged periods just to increase vitamin D.
(The Week)
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