Vitamin D (25-hydroxyvitamin D): Normal Range, What High & Low Levels Mean

The test measures 25-hydroxyvitamin D — also called 25-OH vitamin D or calcidiol — the main form of vitamin D circulating in your blood. Your liver produces this molecule from the vitamin D your skin makes during sun exposure and from what you take in through food or supplements. Because it captures both of those sources together, it gives the clearest picture of your overall vitamin D status. Doctors use this single marker to understand whether your body has enough vitamin D to support calcium absorption, bone strength, and immune function. Discuss your specific result with your healthcare provider to understand what it means for you personally.

According to the Endocrine Society, a sufficient vitamin D level for adults sits between 30 and 100 ng/mL. Levels from 20 to 29 ng/mL are classified as insufficient — lower than ideal but not severely so. A reading below 20 ng/mL is defined as deficient. At the other end, levels above 100 ng/mL are considered potentially toxic. Keep in mind that individual laboratories may use slightly different reference intervals, and what counts as optimal for you can depend on factors like your age, health conditions, and any symptoms you have. Your healthcare provider is the right person to interpret exactly where your number falls for your situation.

The most common reason vitamin D climbs above 100 ng/mL — the threshold the Endocrine Society flags as potentially toxic — is taking excessive amounts of vitamin D supplements over time. Certain medical conditions can also push levels up, including granulomatous diseases such as sarcoidosis, tuberculosis, and histoplasmosis, which convert vitamin D to its active form without the body's usual regulatory checks. Some types of lymphoma and, rarely, primary hyperparathyroidism can have the same effect. Because toxicity from sun exposure alone is not considered a realistic concern, a very high result almost always prompts questions about supplement use or an underlying condition. Talk to your healthcare provider about what may be driving your elevated level.

Many factors can pull vitamin D levels below the sufficient range. Limited sun exposure is a key driver — whether from working indoors, living at high latitudes, or covering your skin. Darker skin pigmentation naturally reduces how much vitamin D your skin synthesizes, and this capacity also declines with age. Because vitamin D is fat-soluble, it can become sequestered in body fat, making obesity a contributing factor. Conditions that impair absorption — such as celiac disease, Crohn's disease, and cystic fibrosis — prevent the gut from taking in enough dietary vitamin D. Chronic kidney disease and liver disease interfere with how the body processes vitamin D. A vegan diet without supplementation and certain medications, including corticosteroids and some antiepileptics, can also lower levels. Speak with your healthcare provider to identify what might be affecting your result.

Low vitamin D can show up as bone pain and tenderness (a condition in adults called osteomalacia), muscle weakness and cramps, persistent fatigue, low mood, and more frequent infections, since vitamin D plays a role in immune function. In children, severe deficiency can cause rickets, which affects bone development. On the opposite end, very high vitamin D levels may cause nausea, vomiting, weakness, fatigue, frequent urination, excessive thirst, and kidney stones — effects driven by the excess calcium that builds up when vitamin D is too high. Confusion and disorientation can occur in severe cases. Many of these symptoms overlap with other conditions, so a blood test is the only reliable way to know your actual vitamin D status. Always discuss any symptoms with your healthcare provider.

Retesting is a common next step after a low or high result, especially if you have changed your sun exposure habits, adjusted your diet, or started or stopped a supplement. The timing of a follow-up test matters — vitamin D levels shift gradually over weeks to months rather than days, so testing too soon may not capture meaningful change. The right retesting interval depends on your starting level, what changes you made, and any underlying health conditions that affect how your body processes vitamin D. There is no single answer that fits everyone, which is why a personalised plan from your healthcare provider is the most reliable guide for deciding when to recheck your level.