Improving vitamin D deficiency typically requires a combination of supplementation, sun exposure, and dietary changes, with the specific approach depending on how low your levels are. Most people with a confirmed deficiency need at least 1,000 to 2,000 IU of vitamin D daily for several weeks to bring their blood levels above 30 ng/mL, the threshold most experts consider adequate. Here’s how to approach it across every lever you can pull.
Know Your Starting Level
A simple blood test measuring your serum 25-hydroxyvitamin D tells you where you stand. Levels below about 20 ng/mL are generally considered deficient, 20 to 29 ng/mL is insufficient, and 30 ng/mL or above is adequate for most people. The lower your starting point, the more aggressive your repletion plan needs to be. If your level is between 8 and 16 ng/mL, you’ll likely need around 2,000 to 2,750 IU daily for eight weeks to climb above 30. If you’re closer to 24 ng/mL, a daily dose of 750 to 1,160 IU over the same period is often enough.
Without testing, you’re guessing. Because vitamin D is fat-soluble and accumulates in the body, knowing your baseline helps you avoid both under-dosing (which wastes time) and over-dosing (which carries real risks at extreme levels).
Choose the Right Supplement
Vitamin D comes in two supplement forms: D3 (from animal sources) and D2 (from plant or fungal sources). They look similar on a molecular level, differing only in their side-chain structure, but they don’t perform identically in your body. D3 appears to be the preferred form for the liver enzyme that converts vitamin D into its circulating form. D2 also gets broken down faster through an inactivation step, which reduces how long it stays effective. A systematic review and meta-analysis in The American Journal of Clinical Nutrition confirmed that D3 raises blood levels more effectively than D2 at the same dose. If you have the choice, D3 is the better option. D2 still works, but you may need higher doses to get the same result.
For people with severe deficiency, the Endocrine Society recommends 50,000 IU once per week for eight weeks as a loading protocol. This is a prescription-level dose, not something to self-prescribe. After repletion, a daily maintenance dose in the range of 1,000 to 2,000 IU keeps most people in the adequate range long-term.
Take It With Fat
Vitamin D is fat-soluble, meaning it dissolves in fat rather than water. Your gut absorbs it significantly better when dietary fat is present at the same time. Taking your supplement with your largest meal of the day, or alongside foods like eggs, avocado, nuts, or olive oil, is one of the simplest ways to boost how much you actually absorb. Some vitamin D does get absorbed without fat, but you’re leaving absorption on the table if you take it on an empty stomach or with just coffee.
Magnesium also plays a supporting role. Your body needs magnesium to convert vitamin D into its active form, so if you’re low in magnesium (which is common), your vitamin D supplementation may be less effective than expected. Eating magnesium-rich foods like spinach, pumpkin seeds, almonds, and black beans can help close that gap.
Use Sunlight Strategically
Your skin manufactures vitamin D when UVB rays hit it directly, and this remains the most natural way to maintain levels. Exposing bare arms and legs to midday sun (between 10 a.m. and 3 p.m.) for 5 to 30 minutes, twice a week, can be sufficient to meet vitamin D needs for many people. The wide range in that recommendation exists because several factors dramatically change how much vitamin D your skin produces.
Skin pigmentation is the biggest variable. People with darker skin need up to ten times longer in the sun to synthesize the same amount of vitamin D as people with fair skin, because melanin acts as a natural sunscreen that slows UVB absorption. Latitude matters too. If you live above about 37 degrees north (roughly a line from San Francisco to Richmond, Virginia), UVB rays are too weak during winter months to trigger meaningful vitamin D production, no matter how long you stay outside. Cloud cover, sunscreen, and clothing all reduce synthesis as well.
Sun exposure is a useful supplement to your strategy, but for most people with a confirmed deficiency, it’s not enough on its own, especially during fall and winter.
Add Vitamin D-Rich Foods
Very few foods naturally contain significant vitamin D, which is a big part of why deficiency is so common. The richest natural sources include fatty fish like salmon, mackerel, sardines, and trout, which can provide 400 to 700 IU per serving. Cod liver oil is exceptionally concentrated, delivering over 1,000 IU per tablespoon. Egg yolks contain a modest amount, roughly 40 to 50 IU each, with the vitamin D concentrated entirely in the yolk.
Fortified foods fill some of the gap. Most milk sold in the U.S. is fortified with about 100 to 120 IU per cup, and many orange juices, cereals, and plant-based milks add similar amounts. UV-exposed mushrooms are one of the few plant-based sources, though they primarily provide D2 rather than D3. Realistically, diet alone rarely provides enough to correct a deficiency. Think of food as a supporting layer on top of supplementation and sunlight.
How Long Recovery Takes
If you’re starting from a significantly low level (under 20 ng/mL), expect the repletion phase to take about 8 to 12 weeks of consistent supplementation before your blood levels reach the adequate range. A recheck at that point confirms whether your dose is working. Some people need to adjust upward, particularly those with obesity (vitamin D gets sequestered in fat tissue), digestive conditions that impair fat absorption, or those taking medications that speed up vitamin D metabolism.
Once you’ve reached adequate levels, the shift is from correction to maintenance. Most adults do well on 1,000 to 2,000 IU daily going forward, though people with risk factors for deficiency may need more. Annual or biannual blood tests help you stay on track without guessing.
Avoiding Too Much
Vitamin D toxicity is rare but real, and it only happens from supplements, never from sun exposure or food. For most people, symptoms of toxicity only appear at daily doses above 10,000 IU taken over extended periods. The core danger is that excess vitamin D causes abnormally high calcium levels in the blood, which can damage the kidneys, bones, and soft tissues over time.
Warning signs include frequent urination, excessive thirst, nausea, decreased appetite, constipation, muscle weakness, fatigue, and confusion. If you’re taking high-dose supplements, especially anything above 4,000 IU daily without medical guidance, periodic blood monitoring is worth the effort. The goal is a serum level in the 30 to 50 ng/mL range for most people. Going higher doesn’t provide additional benefits and starts to carry risk.