The most effective ways to get more vitamin D are sunlight exposure, eating specific foods, and taking supplements. Most people need a combination of at least two of these, especially during winter months. The recommended daily intake for most adults is 600 IU (15 mcg), rising to 800 IU (20 mcg) for adults over 70.
Sunlight: The Most Efficient Source
Your skin produces vitamin D when ultraviolet B (UVB) rays hit it directly. During months when the UV index is 3 or above (roughly spring through early fall in most of the U.S.), exposing your face, arms, and hands for just a few minutes on most days is enough for people with lighter skin tones. If you have naturally very dark skin, you may need three to six times that exposure because melanin slows UVB absorption.
Winter is a different story. If you live north of about 42 degrees latitude (think Boston, Detroit, or Eugene, Oregon), the sun sits too low on the horizon from November through February for your skin to produce any vitamin D at all. During those months, or anytime the UV index drops below 3, you’d need two to three hours per week of direct exposure to your face, arms, and hands to make enough. For most people, that’s impractical in cold weather, which is why food and supplements become essential in winter.
Sunscreen does reduce vitamin D production. SPF 15 filters out 93 percent of UVB rays, and SPF 30 blocks 97 percent. In practice, though, most people don’t apply sunscreen thickly or evenly enough to block all synthesis. The brief, casual sun exposure you get walking to your car or eating lunch outside still contributes, even on days you wear sunscreen for longer outdoor stretches.
Best Food Sources of Vitamin D
Very few foods contain significant vitamin D naturally, and even the best ones require some planning to eat regularly. Here’s what delivers the most per serving:
- Cod liver oil (1 tablespoon): 1,360 IU. By far the most concentrated dietary source, though the strong flavor isn’t for everyone.
- Rainbow trout, farmed (3 ounces cooked): 645 IU. A single serving gets you past the full daily recommendation.
- Sockeye salmon (3 ounces cooked): 570 IU. Another serving that nearly covers a full day.
- Fortified milk, 2% (1 cup): 120 IU. Soy, almond, and oat milks typically provide 100 to 144 IU per cup when fortified.
- Fortified cereal (1 serving): 80 IU.
- Eggs (1 large, scrambled): 44 IU. The vitamin D is entirely in the yolk.
- Canned sardines (2 sardines): 46 IU.
The takeaway from these numbers is clear: unless you’re eating fatty fish several times a week, food alone probably won’t cover your needs. A glass of fortified milk and an egg together provide roughly 164 IU, barely a quarter of the daily recommendation. Fortified foods help fill gaps, but they’re supporting players rather than the main source for most people.
Choosing the Right Supplement
Vitamin D supplements come in two forms: D2 (ergocalciferol, plant-derived) and D3 (cholecalciferol, typically from animal sources like lanolin, though vegan versions made from lichen exist). D3 tends to raise blood levels somewhat more effectively than D2. A meta-analysis comparing the two found D3 produced a numerically greater increase in blood levels, though the difference wasn’t statistically significant across all studies. D3 is the more widely recommended form and the one you’ll find in most supplements.
For general maintenance, 600 to 1,000 IU daily is a typical range for adults. People who are already deficient often take higher doses for a set period to bring their levels up, then switch to a maintenance dose. The tolerable upper limit for adults is 4,000 IU per day. Going beyond that without medical supervision raises the risk of calcium buildup, which can cause nausea, kidney problems, and other complications over time.
How to Absorb More of What You Take
Vitamin D is fat-soluble, meaning your body absorbs it through the same pathway it uses to digest dietary fat. Taking a supplement on an empty stomach or with a fat-free meal means a meaningful portion passes through unabsorbed. The fix is simple: take your vitamin D with a meal that includes some fat. Avocado, nuts, olive oil, cheese, or even the fat in a normal breakfast with eggs will do the job.
Magnesium plays a less obvious but equally important role. Every enzyme your body uses to convert vitamin D into its active form requires magnesium as a cofactor. These conversions happen in the liver and kidneys, and without enough magnesium, the process stalls. Research published in the Journal of Osteopathic Medicine found that vitamin D supplementation produced a significant increase in blood levels only when paired with adequate magnesium. Neither vitamin D nor magnesium alone was enough. Magnesium also influences how many vitamin D receptors your cells produce, so a deficiency can reduce your body’s ability to use the vitamin D that’s already circulating.
Good magnesium sources include pumpkin seeds, spinach, almonds, black beans, and dark chocolate. Many adults fall short of the recommended 310 to 420 mg per day, so this is worth paying attention to if your vitamin D levels aren’t responding to supplementation.
Who Needs to Pay Extra Attention
Several groups face a higher risk of vitamin D deficiency. People with darker skin need significantly more sun exposure to produce the same amount. Older adults produce less vitamin D in their skin and often spend less time outdoors. People with higher body fat may need more because vitamin D gets sequestered in fat tissue, reducing the amount available in the bloodstream. Anyone who works indoors during daylight hours, wears clothing covering most of their skin, or lives at northern latitudes during winter is also at increased risk.
Certain digestive conditions that affect fat absorption, including Crohn’s disease and celiac disease, can also impair vitamin D uptake from both food and supplements. If you fall into any of these categories, a blood test is the most reliable way to know where you stand and how aggressively to supplement.
A Practical Daily Strategy
For most people, the best approach combines small amounts of sun exposure when the season allows, a couple of servings of vitamin D-rich or fortified foods each day, and a supplement to close the gap. During summer, a few minutes of midday sun on exposed skin plus a normal diet may be enough. During winter, especially at northern latitudes, a daily D3 supplement of 600 to 1,000 IU taken with a fat-containing meal becomes the backbone of your intake.
Pair that with magnesium-rich foods or a magnesium supplement, and you give your body what it needs to actually convert and use the vitamin D you’re taking in. This combination of sun, food, and smart supplementation is more effective than relying on any single source alone.