Most adults need 600 IU (15 mcg) of vitamin D per day, and adults over 70 need 800 IU (20 mcg). These are the Recommended Dietary Allowances set by the National Academies of Sciences, Engineering, and Medicine, based on the assumption that you’re getting minimal sun exposure. Your actual needs may be higher depending on your body weight, where you live, and how much time you spend outdoors.
Daily Recommendations by Age
Vitamin D recommendations vary across the lifespan, but the range is narrower than most people expect. Infants from birth through 12 months need 400 IU daily. From age 1 all the way through age 70, the recommendation holds steady at 600 IU. After 70, it increases to 800 IU to account for the skin’s declining ability to produce vitamin D from sunlight and changes in how the kidneys activate it.
During pregnancy and breastfeeding, the standard recommendation remains 600 IU per day. However, if a blood test reveals a deficiency, the American College of Obstetricians and Gynecologists considers 1,000 to 2,000 IU per day safe for pregnant women, with most experts agreeing that up to 4,000 IU is acceptable.
Why Many People Need More Than the RDA
The official RDA is designed to meet the needs of 97.5% of the healthy population, but several common factors can push your personal requirement higher. Body weight is one of the biggest. Because vitamin D is fat-soluble and gets stored in fat tissue, people with obesity (a BMI of 35 or above) respond roughly 40% less effectively to the same dose compared to people at a lower weight. A study published in Endocrine Practice found that the body’s response to each microgram of vitamin D was 0.40 nmol/L per day in obese participants versus 0.66 nmol/L per day in non-obese participants. In practical terms, if 600 IU works for someone at a healthy weight, a person with obesity may need closer to 840 to 1,000 IU to reach the same blood level.
Other factors that increase your needs include having darker skin (more melanin slows vitamin D production from sunlight), living at higher latitudes where winter UV exposure is weak, spending most of your time indoors, and being over 65. If several of these apply to you, the standard 600 IU may not be enough to keep your blood levels in a healthy range.
How Sunlight Fits In
Your skin produces vitamin D when exposed to UVB rays, and for many people this is the single largest source. The general guideline: exposing your face, hands, and arms to sunlight without sunscreen two to three times per week, for about half the time it would take your skin to begin turning pink, produces a meaningful amount. For someone with fair skin at a UV index of 7 (a typical summer midday), that works out to roughly 12 minutes per session.
The catch is that this math changes dramatically with the seasons and your location. In much of the northern United States, Canada, and northern Europe, UVB rays are too weak from roughly October through March to trigger any significant vitamin D production in the skin. During those months, food and supplements become your only reliable sources.
Food Sources Worth Knowing
Very few foods naturally contain vitamin D in meaningful amounts. Fatty fish is the standout: a 3-ounce serving of cooked salmon provides around 500 to 600 IU, and the same amount of canned tuna offers about 150 IU. Cod liver oil packs the most concentrated dose at roughly 1,360 IU per tablespoon, though the taste limits its appeal. Egg yolks contain about 40 IU each, so you’d need to eat 15 a day to hit 600 IU from eggs alone.
Fortified foods fill some of the gap. A cup of fortified milk or plant-based milk typically provides 100 to 120 IU, and many breakfast cereals add a similar amount per serving. Even with a diet rich in these foods, most people fall short of 600 IU from food alone, which is why supplements are so common.
D2 vs. D3 Supplements
Vitamin D supplements come in two forms. D3 (the form your skin makes from sunlight) is generally more effective at raising and maintaining blood levels than D2 (the plant-derived form). Both work, and both will improve a low level, but if you’re choosing between the two, D3 is the better option for most people. D2 tends to be cheaper and is the form used in many prescription supplements, but research consistently shows D3 raises blood levels more reliably over time.
The Role of Magnesium
Your body can’t fully activate vitamin D without magnesium. The enzymes that convert vitamin D into its usable form are magnesium-dependent, and a randomized trial found that magnesium supplementation actually influenced vitamin D blood levels. In participants whose vitamin D started near 30 ng/mL, adding magnesium raised their levels. Interestingly, in those with higher baseline vitamin D (30 to 50 ng/mL), magnesium helped regulate levels downward, suggesting it acts as a kind of optimizer. If you’re supplementing vitamin D and your levels aren’t budging, low magnesium intake could be part of the reason. Good magnesium sources include nuts, seeds, leafy greens, and whole grains.
Safe Upper Limits
The tolerable upper intake level for adults is 4,000 IU per day. This isn’t a target; it’s the ceiling considered safe for long-term daily use without medical supervision. For infants up to 6 months, the upper limit is 1,000 IU; for infants 6 to 12 months, it’s 1,500 IU; and for children 1 to 8, it ranges from 2,500 to 3,000 IU depending on age.
Toxicity is rare and generally only occurs at sustained doses above 10,000 IU per day. When it does happen, the problem isn’t the vitamin D itself but the dangerously high calcium levels it causes. Symptoms include frequent urination, excessive thirst, nausea, constipation, muscle weakness, fatigue, and confusion. These resolve once supplementation stops, but in severe cases the excess calcium can damage the kidneys. You cannot get vitamin D toxicity from sunlight or food. It only happens from supplements.
How to Know If You’re Getting Enough
A simple blood test measuring your 25-hydroxyvitamin D level is the only reliable way to check your status. Most labs and medical organizations consider levels below 20 ng/mL deficient and levels between 20 and 29 ng/mL insufficient. A level of 30 ng/mL or above is generally considered sufficient for bone and overall health, though some researchers argue the sweet spot is between 40 and 60 ng/mL. Levels consistently above 50 ng/mL from supplementation may not offer additional benefits and could carry risks over time.
If you spend limited time outdoors, live in a northern climate, have darker skin, or carry extra weight, a blood test is especially useful. It takes the guesswork out of choosing a dose and lets you adjust based on your actual levels rather than population averages.