Eating lots of orange and dark green veggies such as carrots, sweet potatoes and green beans may be tied to less disease and longer life, suggests a new study.

This time it is not the beta-carotene in vegetables that has the spotlight, but rather its cousin: alpha-carotene. Both are members of the carotenoid antioxidant family. Scientists believe carotenoid antioxidants promote health by counteracting oxygen-related damage to DNA.

Consumption of fruits and vegetables has long been associated with lower risks of health problems such as cancer and heart disease, said Dr. Chaoyang Li of the U.S. Centers for Disease Control and Prevention, in Atlanta, in e-mail to Reuters Health.

However, it is still not clear which elements contribute to the health effects or how they do so, he added, pointing to recent studies that have found no apparent benefit for beta-carotene supplements.

To investigate the merits of oft-ignored alpha-carotene, Li and his colleagues analyzed information on more than 15,000 people who were participating in the Third National Health and Nutrition Examination Survey Follow-up Study. All of them provided blood samples at the start of the study, along with other medical and lifestyle information.

By the end of the 14-year study, nearly 4,000 participants had died. The researchers found that the more alpha-carotene participants had in their blood at the start of the study, the lower their risks of disease and death.

For example, compared to individuals with only trace amounts of alpha-carotene in their blood, those with the highest levels had up to a 39 percent lower risk of dying, the researchers reported in the Archives of Internal Medicine.

The findings held after accounting for risk factors such as age and smoking, and were also similar when looking specifically at rates of death due to heart disease and cancer.

Still, the researchers caution that the link does not prove that alpha-carotene deserves the credit.

“Alpha-carotene may be at least partially responsible for the risk reduction,” Li said. “However, we are unable to rule out the possible links of other antioxidants or other elements in vegetables and fruits to lower mortality risk.”

“Alpha-carotene has a lot of overlapping chemical properties with beta-carotene, as well as the same perceived mechanisms of effect,” added Howard Sesso of the Harvard School of Public Health, in Boston, who reviewed the findings for Reuters Health. “In fact, it’s hard to disentangle the two from each other. They tend to travel together.”

Carrots, carotenoid’s namesake, are a key source of both.

Li did highlight some potential evidence for a difference between the two. Laboratory studies have hinted that alpha-carotene is about 10 times more effective at inhibiting some forms of brain, liver and skin cancer than beta-carotene.

“We don’t know how this is going to translate into practice yet, but it is encouraging,” said Sesso. “If nothing else, these results reinforce the point that there is likely little downside to increasing your fruit and veggie intake.”

SOURCE: Archives of Internal Medicine, online November 22, 2010.