Vitamin D deficiency: what the blood number means

Wild Foods Editorial Team · Updated October 13, 2026 · Sources checked October 13, 2026

Vitamin D deficiency, on the NIH fact sheet, is a serum 25-hydroxyvitamin D level below 30 nmol/L, or 12 ng/mL. That cutoff is tied to rickets in children and osteomalacia in adults. A level from 12 to under 20 ng/mL is called inadequate, not deficient. The adult RDA is 600 IU through age 70, and 800 IU after that, set as if sun exposure were minimal.

What blood level counts as vitamin D deficiency?

The NIH Office of Dietary Supplements uses serum 25-hydroxyvitamin D, written 25(OH)D. Below 30 nmol/L (12 ng/mL) is associated with deficiency. From 30 to under 50 nmol/L (12 to under 20 ng/mL) is generally considered inadequate for bone and overall health. At or above 50 nmol/L (20 ng/mL) is generally considered adequate in healthy people.

Those bands come from the Institute of Medicine's 2010 report, which the fact sheet reprints as Table 1. The same page says an optimal level for bone and general health has not been established, because it likely varies by life stage, ancestry, and the measure being used. A lab printout and a blog are not the same reading. Assays also differ across labs.

The table is on the NIH Office of Dietary Supplements vitamin D fact sheet, updated June 27, 2025.

25(OH)D	How the fact sheet reads it
Under 12 ng/mL	Associated with deficiency
12 to under 20 ng/mL	Generally considered inadequate
20 ng/mL or higher	Generally considered adequate in healthy people
Over 50 ng/mL	Linked to potential adverse effects, especially over 60

What does deficiency look like?

In children, the fact sheet says deficiency shows up as rickets: bone tissue that does not mineralize properly, so bones stay soft and the skeleton can deform. In adolescents and adults, the named condition is osteomalacia.

A low week of energy is not on that list. Deficiency, in this fact sheet, is a bone finding tied to a low blood level, limited sun, poor absorption, or kidneys that cannot convert 25(OH)D to the active form. Diets low in vitamin D are more common in people who avoid milk, including those with lactose intolerance or a milk allergy, and in people who eat an ovo-vegetarian or vegan pattern.

How much vitamin D do adults need?

The adult RDA is 15 mcg (600 IU) from ages 19 to 70, for both men and women. After age 70 it rises to 20 mcg (800 IU). The Food and Nutrition Board set those numbers on the assumption of minimal sun exposure, even though sunlight is a major source for some people.

The RDA is the average daily intake estimated to meet the needs of nearly all healthy people in that group, about 97 to 98 percent. It is a planning number. It is not a blood result, and falling short of it for a week is not the same finding as a 25(OH)D under 12 ng/mL.

Who is more likely to run low?

The fact sheet names breastfed infants, older adults, people with limited sun exposure, people with dark skin, people with conditions that limit fat absorption, and people with obesity or a history of gastric bypass.

Getting enough from unfortified food alone is described as difficult. Fortified foods and some sunlight are called essential for many people. Some groups might need a supplement to meet the requirement. Being in a higher-risk group is a reason to ask a clinician for a level, not a reason to pick a dose from a product page.

Can supplemental vitamin D go too high?

Toxicity is almost always from supplements, not from sun or ordinary food. The fact sheet says it can cause high blood calcium, high calcium in urine, and high 25(OH)D. In extreme cases it may lead to kidney failure, calcification of soft tissue, irregular heartbeat, and death.

The adult Tolerable Upper Intake Level is 100 mcg (4,000 IU). The Food and Nutrition Board noted that signs of toxicity are unlikely below 250 mcg (10,000 IU) a day, and still advised against serum 25(OH)D above about 50 to 60 ng/mL. Levels above 50 ng/mL are already flagged for potential adverse effects. Taking calcium supplements with vitamin D supplements may raise the chance of certain adverse effects.

Where does a supplement fit?

Sun, fortified food, and a measured blood level come first. A capsule is one way to add intake. It does not confirm a deficiency, and it does not replace the lab.

Wild K2 and D3 is one product people use when they want vitamin D in a capsule. This page does not list its dose or its other ingredients. If a clinician has already ordered a level, follow that plan.

See Wild K2 and D3

Questions people ask next

Is 20 ng/mL the same as deficiency?

No. On this fact sheet, under 12 ng/mL is the deficiency band. From 12 to under 20 is inadequate. At or above 20 is generally considered adequate in healthy people. Other groups use other cutoffs. This article stays with the table the NIH reprints.

Does the RDA assume you never go outside?

Close. The Food and Nutrition Board based the RDAs on minimal sun exposure, even while noting that sunlight is a major source for some people. The 600 IU and 800 IU figures are intake targets, not a sun prescription.

Is more always better once the level is low?

No. The fact sheet links levels over 50 ng/mL to potential adverse effects, and it places the adult upper intake at 4,000 IU from supplements and food combined in the UL table. A low result is a reason to talk with a clinician, not a reason to stack bottles.

Why do two labs disagree?

The fact sheet says assessing status is complicated by variability in the assays labs use, commonly antibody methods or chromatography. A single number without the method, and without a clinician, is a weak diagnosis.

Sources

• Vitamin D — Health Professional Fact Sheet, NIH Office of Dietary Supplements. Updated June 27, 2025. Opened October 13, 2026.

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