Sufficient blood levels of 25(OH)D, the measure of vitamin D status, are considered to be greater than or equal to 20-30 ng/mL. Why a range? The National Academy of Medicine chose a conservative cutpoint at 20 ng/mL, while the Endocrine Society says 30 ng/mL. To put this in context, research estimates that 23% of the US population over the age of one have 25(OH)D levels less than 20 ng/ml, and 41% of American adults are below 30 ng/ml. These figures consider all vitamin D inputs, sunshine and diet.
Whether 20 or 30 ng/ml, let me be clear: These two numbers are not goals to aim for. Rather, they are cutoffs to avoid, since lower levels put you into vitamin D insufficient and deficient categories. You want your serum 25(OH)D level to be higher than 20-30 ng/ml, and consistently so. How much vitamin D will that take? Research from the late Robert P. Heaney, M.D. tells us the answer: 100 IU/day of vitamin D increases serum 25(OH)D by about 1 ng/ml in adults.
A little math, y’all: That means you need 2,000 to 3,000 IU/day of vitamin D3 to achieve those minimum cutoffs (20-30 ng/mL) of 25(OH)D. A few important notes: First, these intake levels assume no significant sun exposure (true for many of us during this pandemic) and that the person is a healthy weight. If an individual is overweight or obese, they may require two to three times more vitamin D to achieve that same 25(OH)D level. If a person has regular, significant sun exposure (other health considerations like skin cancer risk may come into play), they will need less vitamin D supplementation.
But remember, greater than 20-30 ng/mL is our goal for vitamin D status. In fact, some researchers and clinicians, including the Endocrine Society, actually recommend aiming for a higher range of 40-60 ng/mL. In adults, that would require 4,000 to 6,000 IU of vitamin D3 each day.
FYI, for all you parents and grandparents out there, the Endocrine Society recommends 1,000 IU per day of vitamin D3 for infants, children, and adolescents (ages zero to 18) to raise their 25(OH)D levels above 30 ng/ml. For young children, liquid or gummy forms of vitamin D are available. For adults and children, you should know that the vitamin D3 form is superior to D2, as the former raises and maintains serum 25(OH)D levels much more efficiently.