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. Sunlight does more than make vitamin D.
Outdoor daylight has several potential benefits beyond vitamin D:
• Circadian rhythm: helps synchronise the body clock.
• Sleep: appropriately timed daytime light can strengthen the day–night signal and support healthier sleep timing.
• Alertness and concentration: bright daytime light promotes wakefulness.
• Mood: greater exposure to natural outdoor light is associated with better mood and may be particularly relevant in people vulnerable to seasonal mood changes.
• Healthy behaviour: going outdoors often means more walking, exercise and social interaction.
However, sunlight should not be oversold as a cure for cardiovascular disease, depression or other illnesses. Many of these associations are influenced by overall lifestyle and other factors.
Who actually needs a vitamin D blood test?
A vitamin D test measures 25-hydroxyvitamin D [25(OH)D]. Routine testing of every healthy person is not recommended by the 2024 Endocrine Society guideline. The same guideline specifically advises against routine screening simply because someone has dark skin or obesity.
Testing is more appropriate when there is a clinical reason; for example:
• Unexplained bone pain or muscle weakness
• Recurrent or fragility fractures/osteoporosis
• Suspected osteomalacia or rickets
• Malabsorption disorders
• Chronic kidney or liver disease
• Hyperparathyroidism or other disorders affecting calcium/vitamin D metabolism
• Prolonged use of glucocorticoids or certain anti-seizure medicines
• Other conditions in which vitamin D deficiency is particularly likely or clinically important.
An Indian expert consensus also identifies chronic kidney/liver disease, malabsorption, neuromuscular disorders and long-term use of glucocorticoids or certain anti-epileptic drugs among groups in whom assessment deserves particular attention.
When should you take vitamin D supplements?
If a blood test confirms deficiency, supplementation is appropriate, but the dose should depend on the degree of deficiency, age, underlying disease and clinical circumstances.
Healthy adults should not routinely take large 'megadoses' simply because vitamin D is popular. The Endocrine Society recommends that healthy adults below 75 generally follow the standard recommended dietary intake rather than routinely taking higher doses.
Can you get too much vitamin D?
Absolutely. Vitamin D toxicity is usually caused by excessive supplementation, not sunlight. Very high vitamin D levels can cause hypercalcemia.
Warning symptoms include: Nausea, vomiting, constipation, excessive thirst, frequent urination, weakness, confusion, kidney stones and kidney dysfunction. Severe toxicity can cause cardiac and neurological complications.
Don't think of sunlight simply as a vitamin D tablet from the sky. Get bright outdoor daylight regularly, especially earlier in the day, for your biological clock, alertness and overall well-being. For vitamin D, remember that UVB exposure varies greatly, so there is no single 'ideal' number of minutes for every Indian.
The opinions expressed in this article are those of the author and do not purport to reflect the opinions or views of THE WEEK.
