Fixing a vitamin D deficiency typically involves a combination of supplementation, dietary changes, and sun exposure. The approach depends on how low your levels are: blood levels below 12 ng/mL indicate true deficiency, while levels between 12 and 20 ng/mL are considered inadequate for bone and overall health. Levels at or above 20 ng/mL are generally sufficient for most people.
How to Know If You’re Deficient
Vitamin D deficiency often flies under the radar because its symptoms overlap with so many other conditions. The most common signs are fatigue, bone pain, muscle weakness or cramps, and mood changes like depression. Children with mild deficiency may only notice weak or sore muscles, while severe deficiency in kids can cause rickets, a condition where bones grow incorrectly and bend. In adults, severe deficiency leads to osteomalacia, a softening of the bones that causes deep, aching bone pain.
A simple blood test measuring your 25-hydroxyvitamin D level is the only reliable way to confirm deficiency. If you’re experiencing persistent fatigue or unexplained muscle pain, this test is worth requesting.
Supplementation for Correcting Low Levels
If your blood levels are truly deficient, over-the-counter daily doses probably won’t be enough to catch up. Clinical guidelines recommend a loading phase of 50,000 IU once a week for eight weeks (or roughly 6,000 IU daily) to bring levels back above 30 ng/mL. After that initial correction, a maintenance dose of 1,500 to 2,000 IU per day keeps levels stable. Some protocols suggest continuing with 50,000 IU every other week instead of a daily maintenance dose.
People with obesity, malabsorption conditions like celiac disease or Crohn’s, or those taking medications that interfere with vitamin D metabolism need higher amounts. Guidelines for these groups call for 6,000 to 10,000 IU daily during the correction phase, followed by 3,000 to 6,000 IU daily for maintenance, with ongoing blood monitoring to make sure levels stay on track.
Both vitamin D2 and D3 supplements work for correcting deficiency, though D3 is the form your skin produces naturally and is often preferred. Your provider will likely recheck your blood levels after the eight-week loading phase to confirm the protocol is working.
Getting More From Your Supplements
When you take your supplement matters almost as much as what you take. Vitamin D is fat-soluble, meaning it needs dietary fat to be absorbed properly. Taking your supplement with a meal that contains fat boosts absorption by about 32% compared to taking it on an empty stomach or with a fat-free meal. That difference was measured at peak absorption and remained significant for hours afterward, with absorption running 25 to 40% higher across the measurement window. In practical terms, this means taking your vitamin D with breakfast, lunch, or dinner rather than on its own.
Food Sources of Vitamin D
Very few foods naturally contain meaningful amounts of vitamin D, which is one reason deficiency is so common. Fatty fish like salmon, mackerel, and sardines are the best natural sources. Egg yolks contain smaller amounts. Beyond that, most dietary vitamin D comes from fortified foods: milk, orange juice, breakfast cereals, and some yogurts and plant-based milks have vitamin D added during production.
Even with a diet rich in these foods, it’s difficult to reach therapeutic levels through food alone if you’re already deficient. Diet works better as a maintenance strategy once your levels are back in a healthy range.
Sunlight and Vitamin D Production
Your skin manufactures vitamin D when exposed to UVB radiation from sunlight. 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 enough to maintain adequate levels, depending on several factors.
Skin pigmentation plays a major role. Melanin, the pigment that gives skin its color, competes with the compound in your skin that produces vitamin D. People with darker skin may need up to ten times as long in the sun to produce the same amount of vitamin D as someone with fair skin. This is one reason vitamin D deficiency rates are significantly higher in Black and Hispanic populations.
Where you live matters too. At latitudes around 40 degrees north (roughly the latitude of New York City or Denver), there isn’t enough UVB radiation from November through early March to produce any vitamin D in your skin, no matter how long you’re outside. Ten degrees farther north, in cities like Edmonton or London, that “vitamin D winter” stretches from October through April. If you live in these regions, supplementation during the colder months is essentially the only reliable option.
Who Is Most at Risk
Several groups face a higher likelihood of deficiency. People with higher body fat tend to have lower circulating vitamin D because the vitamin gets sequestered in fat tissue and is less available to the rest of the body. This is why clinical guidelines call for two to three times the standard supplement dose for people with obesity.
People with gastrointestinal conditions that impair fat absorption, including celiac disease, Crohn’s disease, and those who’ve had gastric bypass surgery, absorb less vitamin D from both food and supplements. Older adults produce less vitamin D in their skin and often spend less time outdoors. People who consistently wear clothing covering most of their body, those who work indoors during daylight hours, and anyone living at northern latitudes through winter are also at elevated risk.
Avoiding Too Much Vitamin D
While deficiency is far more common than excess, vitamin D toxicity is possible with aggressive supplementation. Because vitamin D is fat-soluble, your body stores it rather than flushing out the excess the way it does with water-soluble vitamins like vitamin C. Toxicity causes a dangerous buildup of calcium in the blood, leading to nausea, vomiting, weakness, and in severe cases, kidney damage.
You cannot get too much vitamin D from sunlight or food. Toxicity comes from supplements. If you’re taking high-dose supplements (especially the 50,000 IU weekly protocol), periodic blood testing ensures your levels are rising into the target range without overshooting. The tolerable upper limit for adults is generally set at 4,000 IU per day for ongoing use, though short-term higher doses under medical supervision are standard practice for correcting deficiency.