The latest call comes from scientists in Europe and the US, who say that higher intake levels of the vitamin could help protect against conditions such as childhood rickets, adult osteomalacia, cancer, autoimmune type-1 diabetes, hypertension, cardiovascular disease, obesity and muscle weakness.
Writing in the July 28 issue of Experimental Biology and Medicine, the authors propose worldwide policy changes to increase recommended intake levels of the sunshine vitamin. This, they said, would reduce the frequency of certain diseases, increase longevity and reduce medical costs.
"It is high time that worldwide vitamin D nutritional policy, now at a crossroads, reflects current scientific knowledge about the vitamin's many benefits and develops a sound vision for the future," said Anthony Norman, a professor emeritus of biochemistry and biomedical sciences at the University of California, Riverside.
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.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
The authors of the current study note that the best sources of unfortified foods naturally containing vitamin D are animal products and fatty fish and liver extracts like salmon or sardines and cod liver oil. Vitamin D-fortified food sources include milk and milk products, orange juice, breakfast cereals and bars, grain products, pastas, infant formulas and margarines.
Typical recommended daily intakes (RDIs) lie between 200 and 600 international units (IU) per day while more and more science shows the above benefits can be better achieved with levels closer to 2000IU per day without safety concerns.
"Currently, more than half the world's population gets insufficient amounts of this vitamin. At present about half of elderly North Americans and Western Europeans and probably also of the rest of the world are not receiving enough vitamin D to maintain healthy bone," said Norman.
Benefits for all major diseases
Together with co-author Roger Bouillon of the Laboratory of Experimental Medicine and Endocrinology at the Katholieke Universiteit Leuven, Belgium, Norman stresses that if the daily dietary intake of vitamin D is increased by 600-1000 IU in all adults above their present supply, it would bring beneficial effects on bone health in the elderly and on all major human diseases, such as cancer, cardiovascular, metabolic and immune diseases.
In addition, they note that rickets in children could be eradicated if present guidelines for vitamin D intake were strictly implemented for pregnant and lactating women, newborns and children.
Increasing vitamin D dietary intake to 2000 IU per day – and more for subgroups of the world population with the poorest vitamin D status – could also “favourably impact multiple sclerosis, type-1 diabetes, tuberculosis, metabolic syndrome, cardiovascular risk factors and most cancers,” they said.
In adults, it is said vitamin D deficiency may precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases.