You can increase your vitamin D through three main routes: sunlight exposure, food, and supplements. Most people need a combination of at least two of these, since few foods contain meaningful amounts and sun exposure alone is unreliable for much of the year. The recommended daily intake for adults up to age 70 is 600 IU, rising to 800 IU after 70, though many people with low levels need significantly more to catch up.
Sunlight: The Most Efficient Source
Your skin produces vitamin D when ultraviolet B rays hit it directly. Exposing your face, hands, and arms without sunscreen for about 12 minutes, two to three times per week, is enough for adequate production when the UV index is around 7 (a typical summer midday in much of the U.S. and Europe). That 12-minute figure is based on lighter skin tones. The key threshold is receiving about half the dose that would cause mild reddening of your skin.
Several factors shorten or lengthen the time you need. Darker skin contains more melanin, which acts as a natural UV shield and slows vitamin D production considerably. People with very dark skin may need several times longer in the sun to produce the same amount. Latitude matters too: if you live above roughly 35°N (think Atlanta or Los Angeles), UVB rays are too weak from November through February to trigger meaningful production, no matter how long you stay outside. Cloud cover, window glass, and sunscreen all block UVB as well.
This doesn’t mean you should sunbathe for hours. The goal is brief, regular exposure, not prolonged sessions that raise skin cancer risk.
Best Food Sources of Vitamin D
Very few foods are naturally rich in vitamin D, which is why deficiency is so common. The standouts are fatty fish and fish liver oil. A 3-ounce serving of cooked sockeye salmon delivers about 570 IU, nearly a full day’s worth. Farmed rainbow trout is even higher at 645 IU per serving. A single tablespoon of cod liver oil packs 1,360 IU, making it one of the most concentrated food sources available.
Beyond fish, the numbers drop sharply. One large scrambled egg contains just 44 IU, almost all of it in the yolk. Canned sardines offer a modest 46 IU for two fish. That means you’d need to eat more than a dozen eggs a day to hit 600 IU from eggs alone.
Fortified foods help fill the gap. A cup of vitamin D-fortified milk provides about 120 IU. Fortified plant milks (soy, almond, oat) range from 100 to 144 IU per cup depending on the brand. Fortified cereals typically add around 80 IU per serving. These are useful daily additions, but on their own they won’t move the needle much if your levels are already low.
Choosing the Right Supplement
Supplements are the most reliable way to raise your levels, especially if you have limited sun exposure or don’t eat much fish. You’ll find two forms on shelves: D3 and D2. D3 is the clear winner. Research on elderly women with vitamin D deficiency found that D3 is nearly twice as potent as D2 at raising blood levels. Most doctors and dietitians now recommend D3 as the default choice.
For general maintenance, 1,000 to 2,000 IU of D3 daily is a common starting point for adults who aren’t severely deficient. If a blood test shows you’re significantly low, a provider may recommend higher doses for 8 to 12 weeks to replenish your stores faster, then a lower maintenance dose afterward.
Vitamin D is fat-soluble, so taking your supplement with a meal that contains some fat improves absorption. A handful of nuts, avocado on toast, or even a glass of whole milk alongside your pill makes a difference compared to taking it on an empty stomach.
Why Body Weight Affects Your Dose
If you carry extra weight, you likely need more vitamin D than standard recommendations suggest. Vitamin D gets sequestered in fat tissue, leaving less available in your bloodstream. Research published in PLOS ONE estimated that overweight individuals need about 1.5 times the standard dose, and those with obesity need 2 to 3 times more, to reach the same blood levels as someone at a normal weight. In practical terms, that means a person with obesity might need around 5,000 IU daily to achieve what a normal-weight person gets from 2,000 IU.
Skin Tone and Geography
People with darker skin are at higher risk for vitamin D deficiency because melanin, the pigment that gives skin its color, blocks the same UV rays your body uses to produce the vitamin. This is an evolutionary tradeoff: melanin protects against UV damage and skin cancer, but in regions with less intense sunlight, it becomes a disadvantage for vitamin D production. If you have dark skin and live in a northern climate, supplementation is especially important year-round, not just in winter.
Geography compounds the issue. During winter months at higher latitudes, even people with lighter skin can’t produce vitamin D from the sun. If you live in the northern half of the U.S., most of Canada, or northern Europe, consider supplementing from roughly October through March regardless of skin tone.
Magnesium: The Overlooked Co-factor
Taking vitamin D without enough magnesium in your system can limit how well the vitamin actually works. Magnesium serves as a co-factor for the enzymes that activate vitamin D in your liver and kidneys. It’s also required for vitamin D to bind to its transport protein in the blood and for your cells to respond to it properly. In short, if you’re magnesium-deficient, your body may struggle to use the vitamin D you’re taking in.
Many adults don’t get enough magnesium from their diet. Good food sources include dark leafy greens, nuts, seeds, and beans. If you’re supplementing vitamin D and not seeing improvement, inadequate magnesium is one of the first things to consider.
How Long It Takes to See Results
Vitamin D levels don’t change overnight. Most people see a meaningful rise in blood levels after about 6 to 8 weeks of consistent daily supplementation. If you’re starting from a significant deficiency, it can take 3 months or longer to reach sufficient levels. A follow-up blood test after 2 to 3 months of supplementation gives you a clear picture of whether your dose is working or needs adjustment.
Blood levels below 20 ng/mL are generally considered deficient, while 20 to 29 ng/mL is classified as insufficient. Most experts consider 30 ng/mL and above to be sufficient for bone health and general function. Getting a baseline blood test before you start supplementing helps you and your provider choose the right dose rather than guessing.