Got whiplash? Here's a sampling of health studies that have come up with contradictory findings.
Vitamin E and heart disease: A 1993 study following more than 87,000 middle-aged female nurses without heart disease for up to eight years, and another following almost 40,000 male health professionals without heart disease for four years, both found lower rates of heart disease in those taking vitamin E supplements.
But a 4 1/2 -year randomized trial published in 2000 on about 2,500 women and 7,000 men age 55 or older who were at high risk for cardiovascular events found no reduction in cardiovascular disease rates in those who took 400 IU of vitamin E daily.
Vitamin E and cancer: A 1988 epidemiological study in more than 21,000 Finnish men found that the 40% with the highest blood levels of alpha-tocopherol (the predominant form of vitamin E in the blood) had a 36% reduced risk of developing cancer.
But a seven-year randomized trial published in 2005, of more than 700 patients with vascular disease or diabetes mellitus, found no protection from cancer from a daily dose of 400 IU of vitamin E.
Vitamin B6 and folate and cognitive function: A 2005 epidemiological study in almost 500 people age 70 to 79 found that low blood levels of folate or vitamin B6 were associated with worse cognitive function seven years later.
But in a two-year randomized clinical trial published in 2006, healthy older people who took daily doses of folate, vitamin B12 and vitamin B6 showed no improvement in cognitive tests.
Vitamin B6, folate and heart disease: A 1998 study followed about 80,000 women without heart disease for 14 years. It found that the 20% of women taking the top folate dose had a 31% lower risk of coronary heart disease compared with the lowest 20%. The risk reduction was similar for vitamin B6.
But a 2006 analysis of 12 randomized trials in people with cardiovascular or renal disease did not find an effect of folic acid supplements on cardiovascular disease. And a 2004 randomized trial of more than 3,600 adults who had suffered mild strokes found that a high daily dose of folate, vitamin B6 and vitamin B12 had no effect, compared with a low dose, on subsequent strokes and coronary heart disease after two years.