Consuming high amounts of beta-carotene's less well-known antioxidant cousin, alpha-carotene, in fruits and vegetables can lower the risk of dying from all causes, including heart disease and cancer, new research suggests.
Both nutrients are called carotenoids - named after carrots - because of the red, yellow and orange coloring they lend to a range of produce. Once consumed, both alpha- and beta-carotene are converted by the body to vitamin A, although that process is believed to unfold more efficiently with beta-carotene than with alpha-carotene.
However, the new study suggests alpha-carotene may play the more crucial role in defending cells' DNA from attack. This might explain the nutrient's ability to limit the type of tissue damage that can trigger fatal illness, researchers say.
In the study, a team at the US Centers for Disease Control and Prevention (CDC) found that over 14 years of follow-up, most people - regardless of lifestyle habits, demographics or overall health risks - had fewer life-limiting health troubles as their blood concentrations of alpha-carotene rose.
A lot of fruit and veg is good for you
The effect was dramatic, with risks falling from 23 to 39% as an individual's alpha-carotene levels climbed.
"This study does continue to prove the point there's a lot of things in food - mainly in fruits and vegetables that are orange or kind of red in color - that are good for us," said registered dietitian Lona Sandon, American Dietetic Association spokeswoman and an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas.
But Sandon stressed that, right now, the study only proves an association between alpha-carotene and longer life, and can't show cause-and-effect.
The findings are to be published in the Archives of Internal Medicine.
How the study was done
Researchers led by Dr Chaoyang Li, from the CDC's division of behavioural surveillance with epidemiology and laboratory services, note that a host of yellow-orange foods such as carrots, sweet potatoes, pumpkin and winter squash, and mango and melon are rich in alpha-carotene, as are some dark-green foods such as broccoli, green beans, green peas, spinach, turnip greens, collards, kale, Brussels sprouts, kiwi, spinach and leaf lettuce.
These foods fall within the US Department of Agriculture's current dietary recommendations, which highlight the benefits of consuming two to four servings of fruit and three to five servings of vegetables daily.
Li's team focused on more than 15,000 American adults, 20 years of age or older, who took part in the Third National Health and Nutrition Examination Survey. All underwent a medical exam between 1988 and 1994, during which time blood samples were taken. Participants were tracked for a 14-year period through 2006.
By that point, more than 3,800 participants had died. Blood analyses revealed that, compared with those who had blood alpha-carotene levels of between 0 and 1 micrograms per deciliter (mcg/dL), those falling in the range of between 2 and 3 mcg/dL faced a 23% lower risk of death from all causes.
Risk of death for those with alpha-carotene blood levels in the range of between 4 and 5 mcg/dL, between 6 and 8 mcg/dL, and 9 mcg/dL or above dropped 27%, 34% and 39%, respectively, versus those in the 0 to 1 mcg/dL range.
Fruit and veg lowers premature death risk
The team also linked higher blood alpha-carotene levels to a lower risk for dying from the nation's two top killers: cardiovascular disease or cancer.
Li's team said that while more research is needed, the findings generally suggest that eating more fruits and vegetables can help lower your risk for premature death.
Sandon agreed, but cautioned against over-interpreting the findings.
"This is very preliminary," she said. "There haven't been many clinical trials looking into this. And it's always tricky when you're singling out a single nutrient, because components in foods may work individually or synergistically. The question is: Is alpha-carotene acting in conjunction with something else? We don't really know," Sandon explained.
"The alpha-carotene itself is probably not the cause of longer life," she added. "But we can still say that if you're getting more of these kinds of phytonutrients found in foods, this may help you live longer and healthier."
The bottom line, according to Sandon: "I certainly think it would be wrong for people to take away from this that they should set out to specifically consume alpha-carotene. What people should take away from this is that they should go out and eat the foods that have alpha-carotene in them."
And what about nutritional supplements? Li's team pointed out antioxidant supplements currently on the market do not contain much, if any, alpha-carotene, and the study therefore only looked at the impact of consuming the compound via foods.
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