We need far more vitamin D than previously thought, according to two teams of researchers from Canada and the US.

The Recommended Dietary Allowance (RDA) for vitamin D is ten times lower than what we actually need, say two teams of researchers who have challenged the US's National Academy of Sciences (NAS) and the Institute of Medicine (IOM), both responsible for the RDA.

"The error has broad implications for public health regarding disease prevention and achieving the stated goal of ensuring that the whole population has enough vitamin D to maintain bone health," says Dr. Cederic Garland, an adjunct professor at University of California, San Diego.

Currently the RDA for vitamin D established by the IOM is 600 international units per day until we reach 70 years of age, and 800 IU per day thereafter. A Canadian research team reviewed each of the 10 studies the IOM used to arrive at their RDA and their calculations revealed that 600 IU of vitamin D per day puts only half of the amount that they had assumed in the blood.

In scientific terms, that means that 97.5 per cent of individuals will have serum 25 values of vitamin D above 26.8 nmol/L rather than above 50 nmol/L as the IOM had thought.

To get a serum 25 value of vitamin D of at least 50 nmol/L, you could need up to 8895 IU per day, according to the study.

Dr. Garland's team of US researchers wrote a letter confirming the Canadian team's findings, in which they suggest a slightly more conservative RDA. "We call for the NAS-IOM and all public health authorities concerned with transmitting accurate nutritional information to the public to designate, as the RDA, a value of approximately 7,000 IU/day from all sources," wrote Dr.

Garland and his colleagues.

Dr. Garland added that the number is well below the 10,000 IU currently considered safe by the IOM for teenagers and adults.

Two versions exist: Vitamin D2, known as ergocalciferol, and vitamin D3, also known as cholecalciferol, which is thought to be the more potent and favorable version of the two.

Fatty fish, such as salmon, tuna, sardines and cod liver oil contain hearty amounts of vitamin D3, yet most vitamin D3 is synthesized in the skin upon sun exposure, according to the World Health Organization.

Cereals, cheese and milk could be an important source of both types of vitamin D depending upon where you live yet because they are often fortified with synthetic versions and the amounts may vary.

Vitamin D is important for skin, bone and heart health and deficiencies can result in rickets and abnormal skin pigmentation, yet side effects of excess intake are rare and minimal, according to WebMD.