The “call to action” by the UC scientists, led by Anthony Norman, echoes a number of others from leading academics across the globe, and may increase the need for policy makers to review current guidelines for the vitamin. Such increases could also open opportunities for food fortification and supplements.

Current recommended daily intakes (RDIs) of vitamin D are 200 IU for people up to 50 years of age, 400 IU for people between 51 and 70, and 600 IU for over the 70s years.

“The consensus among UC scientists who signed this statement is that 2000 IU per day of vitamin D3, a form of vitamin D, is the appropriate intake for most adult Americans,”​ said Norman.

“This intake is the National Academy of Sciences/Institute of Medicine’s upper limit for daily intake, and is 400 IU less than the National Academy of Sciences/Institute of Medicine’s ‘no adverse health effect’ level. Scientific concerns about this level of intake are minimal, based on the findings of the National Academy of Sciences.” ​

Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.

Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.

“Our consensus on vitamin D is intended to support public health action,”​ said Norman. “The amount of research that is currently available provides us enough information to release such a consensus at this time.”​

Previously, experts have noted that about one billion people are estimated to be vitamin D deficient with children and adults in Europe at particular risk, even more so since very few foods are fortified with the vitamin.

In adults, vitamin D deficiency may precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type 1 diabetes, said the UC scientists.

“While more research on this topic is highly desirable, it should not delay recommending a 2000 IU daily intake of vitamin D for most people,”​ said Norman.

Calls will not be silenced​

Fifteen experts from universities, research institutes, and university hospitals around the world, led by Reinhold Vieth from Toronto's Mount Sinai Hospital, wrote in the American Journal of Clinical Nutrition​ in March 2007 that "international agencies such as the Food and Nutrition Board and the European Commission's Health and Consumer Protection Directorate-General to reassess as a matter of high priority their dietary recommendations for vitamin D, because the formal nationwide advice from health agencies needs to be changed."​

Moreover, researchers from the American University of Beirut-Medical Center, Lebanon said earlier this year that current recommendations for children should be raised to 2,000 IU in order to boost bone health and provide long-term health benefits.

Their study, published in the Journal of Clinical Endocrinology & Metabolism​, found that only children given the equivalent of 2,000 IUs a day of vitamin D3 increased their blood levels of the vitamin to the level considered optimal for adults.