A cutoff of <25 or <30 nmol/L (or 10/12 ng/ml) increases the risk of osteomalacia and nutritional rickets dramatically, and therefore is considered to determine severe vitamin D deficiency [13,14,15,16].
Today, 25(OH)D less than 12 ng/mL is considered evidence of severe vitamin D deficiency.
Although there is no consensus on vitamin D levels required for optimal health -- and it likely differs depending on age and health conditions -- a concentration of less than 20 nanograms per milliliter is generally considered inadequate, requiring treatment.
Therefore, conditions that affect the gut and digestion, like celiac disease, chronic pancreatitis, Crohn's disease, and cystic fibrosis, can reduce vitamin D absorption.
<25 nmol/L – DEFICIENT. 25-50 nmol/L – INSUFFICIENT. 50-75 nmol/L – ADEQUATE. >75 nmol/L – OPTIMUM.
Low levels of vitamin D have been associated with depression, Alzheimer's disease and other dementias, and cognitive decline, as well as psychosis, autism, heart disease, and about 200 other conditions.
A vitamin D level of 17 ng/mL is considered severely deficient. Severe deficiency can occur from prolonged, inadequate intake of vitamin D, limited exposure to sunlight, poor kidney function resulting in impaired conversion of 25(OH)D, or inadequate vitamin D absorption.
If you've been prescribed high-dose vitamin D, work closely with your doctor to monitor your blood levels. It can take three months or more to bring them back up, but once they're good, you can stop the high doses and return to a lower vitamin D supplement for maintenance.
Vitamin D insufficiency may relate to higher levels of anxiety and depression, in turn contributing to the elevated risk of psychosis in this population.
Those with the lowest levels should feel an improvement after just a few days, while those who only need to top up their levels may have to wait a week or two before they begin to feel healthier and more energised.
The blood level of 25(OH)D will peak about 12 hours after a single dose of 50,000 IU.
The severity of vitamin D deficiency is divided into mild, moderate, and severe. [ 18] Mild deficiency: 25-hydroxyvitamin D less than 20 ng/mL. Moderate deficiency: 25-hydroxyvitamin D less than 10 ng/mL. Severe deficiency: 25-hydroxyvitamin D less than 5 ng/mL.
“Adding an over-the-counter vitamin D supplement can make improvements in just three to four months time. Vitamin D with a strength of 1000-2000 international units daily is the recommended dose for most adults,” Dr. Ropte says. Most multivitamins contain vitamin D, so extra supplementation isn't always necessary.
The concurrent presence of fat in the gut enhances vitamin D absorption, but some vitamin D is absorbed even without dietary fat.
"Adequate levels of magnesium in the body are essential for the absorption and metabolism not only of vitamin D but of calcium as well," Dean states. "Magnesium converts vitamin D into its active form so that it can help calcium absorption.
Vitamin D deficiency is most commonly caused by a lack of exposure to sunlight. Some disorders can also cause the deficiency. The most common cause is lack of exposure to sunlight, usually when the diet is deficient in vitamin D, but certain disorders can also cause the deficiency.
Extremely high vitamin D levels are harmful and can cause nausea, vomiting, confusion, excessive thirst and kidney stones. Vitamin D supplements can interact with certain medications, so check with your doctor before starting one.
In a new study published Wednesday in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, researchers examined vitamin D in brain tissue. They found that higher levels of the vitamin were associated with better cognitive function—a stronger memory and a slower progression of cognitive decline.