Vitamin D and calcium were thought to assist in preventing cancer, heart disease and other problems, but this has been questioned by a panel of US and Canadian doctors.
After reviewing about 1,000 studies on the supposed links between low vitamin D levels and higher risk of serious diseases, the panel concluded that they showed inconsistent results, sometimes due to shoddy research methods.
AdvertisementThe experts also issued new guidelines -- the first since 1997 -- for North Americans, saying people should take between 700 and 1,300 milligrams of calcium and anywhere from 600 to 800 international units of vitamin D each day.
Most people "probably don't have vitamin D deficiency, that is the first message," said Glenville Jones, a Canadian doctor who was on the 14-member committee for the US-based Institute of Medicine.
"We think there has been an exaggeration of the public's interest in vitamin D deficiency. (People) should be reassured that vitamin D deficiency is quite rare in North Americans at this point in time."
Just by eating a balanced diet and possibly taking a vitamin supplement in the winter, because sun exposure boosts vitamin D levels, most North Americans would have no difficulty meeting the recommended allotment, he said.
The panel's establishment of new guidelines offer a more solid recommended daily dose than the 1997 approach of suggesting adequate intake (AI) amounts.
The previous recommendations set the amount of calcium at between 210 and 270 milligrams per day for babies, 500 to 1,300 for children aged one to 18, 1,000 per day for adults aged 19-50 and 1,200 for those 50 and older.
For vitamin D, the old recommendations were 200 international units for those under age 50, 400 IU for people 51-70 years old and 600 IU for those over 71.
Jones declined to characterize the new guidelines as higher than before, saying it would be like "comparing apples to pears."
Humans need calcium to help clot blood and for proper functioning of muscles and nerves, and vitamin D is necessary for the body to absorb calcium. Inadequate calcium has been shown to lead to bone fractures and osteoporosis.
The experts noted that some populations are likely to need more Vitamin D than other groups -- including breastfed babies, people with dark skin and those living in northern latitudes where daylight exposure is limited.
Also, the panel did not entirely rule out all benefits from Vitamin D or all studies that suggested beneficial links.
"There are claims about vitamin D in heart disease, in cancer, autoimmune diseases -- you name it, there are claims out there that are not based upon a lot of studies," said Jones.
"Our dilemma is that there are mixed reports that are not all consistent," said Jones, who is a professor of biochemistry at Queens University in Kingston, Ontario.
"Some of the studies are not well controlled," he said.
"We don't want to base public health recommendations upon a mixed conclusion where some studies say there is a benefit in cancer and other studies say they don't," he added.
Jones would not rule out the possibility that future studies could result in more certain benefits toward beating cancer and other diseases, but said "the only really consistent information that was well worth using was information on bone health."
The panel also set upper limits for both calcium (2,000 milligrams per day) and vitamin D (4,000 IUs per day), beyond which point risks such as kidney and tissue damage begin to mount.
"Higher levels have not been shown to confer greater benefits, and in fact they have been linked to other health problems, challenging the concept that 'more is better,'" the report said.