Vitamin D deficiency is the most common nutritional deficiency and likely the most common medical condition in the world.

The major cause of vitamin D deficiency has been the lack of appreciation that the body requires 5- to 10-fold higher intakes than is currently recommended by health agencies.

There is now overwhelming and compelling scientific and epidemiologic data suggesting that the human body requires a blood level of 25(OH)D above 30 ng/mL for maximum health. To increase the blood level to the minimum 30 ng/mL requires the ingestion of at least 1000 IU of vitamin D per day for adults.

In general, there is no downside to increasing either a child's or adult's vitamin D intake.