The best time to get sun for vitamin D production is midday, roughly between 10 a.m. and 2 p.m., when the sun is highest in the sky. This might sound counterintuitive since that’s the same window you’ve been told to avoid, but the science behind it is surprisingly straightforward: a short burst of strong midday sun produces vitamin D more efficiently and with less total skin damage than a longer session of weaker morning or afternoon sun.
Why Midday Sun Is More Efficient
Your skin can only manufacture vitamin D from one specific type of ultraviolet light: UVB. The intensity of UVB radiation peaks when the sun is directly overhead, which is why midday exposure is so effective. When the sun sits lower on the horizon in early morning or late afternoon, its rays travel through more atmosphere, and most of the UVB gets filtered out before it reaches your skin. You’re still getting plenty of UVA radiation during those hours, which contributes to aging and skin damage but does nothing for vitamin D.
This creates a practical tradeoff. To hit the same vitamin D target in weaker morning sun, you’d need to spend significantly more total time exposed, accumulating more UVA damage along the way. Research comparing the action spectra for vitamin D synthesis and sunburn found that exposing as much skin as possible for a short time when the UV index is high produces vitamin D most efficiently while minimizing erythema (sunburn) risk. As a concrete example: when the UV index is 12, it takes less than 5 minutes with your face and arms exposed to produce an adequate daily dose of vitamin D, while sunburn for fair-skinned people wouldn’t begin until about 15 minutes. That gap gives you a comfortable margin.
How Long You Actually Need
Most people need somewhere between 5 and 30 minutes of unprotected midday sun, depending on skin tone, latitude, season, and how much skin is exposed. Darker skin contains more melanin, which blocks UVB, so people with deeper complexions need longer exposure to produce the same amount of vitamin D. Lighter-skinned individuals reach their daily production threshold faster but also burn sooner.
The key is keeping the session brief. You don’t need to tan or turn pink. Once your skin has produced its vitamin D for the day, additional exposure doesn’t create more. It just increases your risk of DNA damage. If you plan to stay outside longer, apply sunscreen or cover up after that initial window.
The UV Index Matters More Than the Clock
Rather than watching the time, check the UV index. This is the single most useful number for planning your sun exposure. The World Health Organization recommends using sun protection when the UV index hits 3 or above, but that same threshold is also the zone where vitamin D production becomes meaningful. When the UV index drops below 2, the sun is too low in the sky for your skin to synthesize any practical amount of vitamin D, no matter how long you stay outside.
Most weather apps display the UV index by the hour. On a summer day in the mid-latitudes, you’ll typically see it climb above 3 by mid-morning, peak around solar noon (which can be closer to 1 p.m. during daylight saving time), and drop back down by late afternoon. That peak window is your sweet spot: high enough for rapid vitamin D production, easy to keep your exposure short.
When the Sun Can’t Help at All
If you live above roughly 37 degrees latitude (think San Francisco, Denver, Athens, Seoul, or anywhere farther from the equator), there are months when midday UVB is simply too weak for vitamin D synthesis. Researchers call this period “vitamin D winter.” During these months, the average clear-sky midday UV index stays below 2, meaning no amount of outdoor time will move the needle on your vitamin D levels. In cities like London, Stockholm, or Toronto, vitamin D winter can stretch from October through March or even longer.
During these months, dietary sources and supplements become the only reliable options. Fatty fish, fortified milk, egg yolks, and mushrooms exposed to UV light all provide some vitamin D, though most people in northern climates find it difficult to hit adequate levels through food alone.
Skin Tone, Age, and Other Variables
Several factors beyond timing affect how much vitamin D your skin produces:
- Skin tone: People with very dark skin may need 3 to 5 times more sun exposure than those with very fair skin to produce the same amount of vitamin D.
- Age: Older adults produce vitamin D less efficiently because the skin thins with age and contains fewer of the precursor molecules that UVB converts.
- Body surface area: Exposing your arms and legs produces far more vitamin D than exposing just your face and hands. The more skin you can safely bare during your brief session, the faster you’ll reach an adequate dose.
- Sunscreen and clothing: Broad-spectrum sunscreen blocks most UVB. Glass windows do the same. You won’t produce vitamin D through a car windshield or office window.
- Cloud cover and pollution: Heavy clouds can cut UVB by 50% or more. Urban smog has a similar filtering effect.
What “Enough” Vitamin D Looks Like
Vitamin D status is measured through a blood test that checks your level of 25-hydroxyvitamin D. Most health authorities consider a reading of 20 ng/mL (50 nmol/L) adequate for the general population. The Endocrine Society previously suggested aiming for above 30 ng/mL, though their revised 2024 statement stepped back from setting a specific optimal number, noting that outcome-specific benefits at higher levels haven’t been firmly established in clinical trials.
What is well established: levels below about 12 ng/mL (30 nmol/L) represent a severe deficiency that can lead to bone disorders like rickets in children and osteomalacia in adults. If you suspect you’re low, a simple blood draw can give you a clear answer. People who spend most of their time indoors, cover most of their skin for religious or cultural reasons, have darker skin, or live at high latitudes are at the greatest risk of falling short.
A Practical Approach
The simplest routine is to step outside for 10 to 15 minutes around midday with your forearms and lower legs exposed, two to three times per week during months when the UV index is above 3. Fair-skinned individuals can cut that time roughly in half. If you’re darker-skinned, you may benefit from slightly longer sessions. After your brief exposure, apply sunscreen or put on a hat and sleeves for the rest of your time outdoors.
During vitamin D winter or if you rarely get midday sun, a daily supplement of 1,000 to 2,000 IU is a common approach that most adults tolerate well. Pairing this with vitamin D-rich foods helps close the gap. The goal isn’t to choose between sun and supplements. It’s to use whichever source is available and practical for the season you’re in.