It is called “bottled sunshine” and claimed to be one of the most effective health supplements on the market. Scores of studies have suggested that it protects against heart disease, cancer, diabetes, high blood pressure, schizophrenia and multiple sclerosis, and a growing number of doctors have recommended it to their patients.
But vitamin D, it turns out, has been oversold. After reviewing more than 1,000 research papers, the authoritative Institute of Medicine in the US has concluded that the high levels often recommended are unnecessary and could even be harmful.
Over recent years the idea that everyone needs extra vitamin D has swept countries on both sides of the Atlantic as scientists and doctors, convinced by the growing body of evidence of the nutrient’s role in a range of diseases, have advocated supplements.
Vitamin D is made naturally in the body from sunlight, which is its main source. It is also found in limited quantities in some foods such as fish and fortified breakfast cereals. As much as half the population is said to have less than optimum levels.
Vitamin D
The gloomy weather and long winter in countries north of 30 degrees latitude, such as the UK, means that a large part of the earth’s population is deficient between October and March.
In the US, sales of vitamin D supplements soared 80 per cent in 2008-09 to $430m (£270m). In 2001 they stood at $40m. Requests for blood tests for vitamin D levels from one company, Quest Diagnostics, surged 50 per cent in the fourth quarter of 2009 alone.
But according to the IoM, the excitement got ahead of the science. Dennis Black, professor of epidemiology at the University of California and an author of the report, said: “Everyone was hoping vitamin D would be kind of a panacea. The number of vitamin D tests has exploded.”
The IoM has now sought to quell the craze. The 14-member expert committee, convened at the request of the US and Canadian governments, was widely expected to increase the recommended blood level of the vitamin, last set in 1997 and based on what was necessary for bone health. Vitamin D is essential for building bones and deficiency in children causes rickets.
Experts had said that the emerging evidence of its role in other diseases meant that the recommended blood level should be increased. But the IoM has rejected the evidence and said that most people are getting enough of the vitamin from sunlight and diet.
“This review found that information about the health benefits [of vitamin D] beyond bone health were from studies that provided often mixed and inconclusive results and could not be considered reliable,” the committee said. They recommend people need 600 international units a day (800 a day over age 70) and warn that doses above 4,000 units a day may be harmful. Vitamin D supplements containing 5,000 units per pill are widely available in the US, and can also be bought in the UK.
“Very high levels of vitamin D (above 10,000 IUs per day) are known to cause kidney and tissue damage. Some preliminary studies offer tentative signals about adverse health effects [at lower levels]“, they add.
Oliver Gillie, of the UK Health Research Forum, said there was a greater need for vitamin D supplementation in the UK because of our poorer weather and fewer vitamin D enriched foods.
“American adults are already getting about 300 international units from sun and fortified milk and orange juice, whereas in the UK we get an average of only 150 IUs per day from all sources. So this means we need to take 450 IUs per day to fall in line with the IoM recommendation,” he said.
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Taking large doses of vitamin D supplements may not reduce women’s risk of frailty later in life, according to a new study.
In fact, the study found that both low and high levels of vitamin D in the blood were associated with an increased likelihood of frailty among older women. The researchers considered women to be frail if they had symptoms such as a slow walking speed, weak hand grip or exhaustion.
While the link between high levels of vitamin D and frailty was not consistent over time, there was no evidence that higher levels were protective, the researchers say.
The results come on the heels of a report released last week by the Institute of Medicine issuing new guidelines for daily vitamin D intake. Older adults need about 800 international units (IU) a day — an amount achievable without taking supplements — and most Americans and Canadians get enough, the report said.
The new findings underscore the need for more well-designed clinical trials in order to evaluate the health effects of vitamin D supplements, the researchers said.
Although vitamin D deficiency has been linked with adverse health effects, that doesn’t mean that more vitamin D is beneficial, said study researcher Dr. Kristine Ensrud, a professor of medicine and epidemiology at the University of Minnesota.
“Sometimes people get so convinced that something’s good for you,” Ensrud said. “In a way, vitamin D supplementation sort of got put in the ‘water supply’ when the evidence wasn’t really wasn’t behind that.”
Vitamin D deficiency can lead to weakness and slowness, both components of frailty. Some experts have recommended vitamin D supplements for older adults whose blood levels of vitamin D are below 30 nanograms per milliliter (ng/ml), the researchers said. This would likely require taking supplements of 1000 to 2000 IU of vitamin D per day.
Ensrud and her colleagues measured the vitamin D blood levels of 6,307 women 69 years and older, and also determined how frail the women were.
Women with vitamin D levels less than 20 ng/ml and greater than 30 ng/ml had higher odds of being frail than women whose vitamin D levels fell in between those marks. This association held even when the researchers included only the vitamin D in the blood produced by the body in response to sunlight. They performed this analysis to rule out the possibility that frail women might be prescribed vitamin D supplements.
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The researchers also looked at the impact of vitamin D levels over time among 4,551 women who were not frail at the beginning of the study. They examined the frailty status of these women 4 1/2 years later. In this case, only vitamin D levels lower than 20 ng/ml were associated with increased risk of frailty or death later in life.
The researchers said that the fact that they didn’t find a link between high vitamin D levels and frailty after the 4.5-year study period may mean the association between these two factors found in the earlier part of the study was not a true link. However, it might also be that there were too few women in the follow-up study to observe a link later on, Ensrud said.
Nonetheless, even over time, having high levels of vitamin D at the study’s start didn’t lessen a woman’s chances of later developing frailty, Ensrud said.