Need another reason to eat your greens (and yellows and oranges) as part of a healthful diet in the New Year? A large U.S. study has found that adults with higher concentrations of serum alpha-carotene in their blood were likely to live longer than those who had lower levels.

Research around carotenoids (phytochemicals that also include beta-carotene, lycopene and others) has yielded mixed results. Cheering of beta-carotene's purported disease-fighting abilities quieted down after years of studies failed to show that supplements reduced risk of cancer, cardiovascular disease or type-2 diabetes (all diseases linked to free-radical damage, which antioxidants, such as carotenoids, are thought to help neutralize).

Nevertheless, increased consumption of fruits and vegetables (which are often high in carotenoids) continue to be linked to a longer, healthier life, often regardless of other lifestyle factors. So researchers are now busy chasing down other components of these foods.

The recent alpha-carotene research is one such study. It assessed the blood levels of serum alpha-carotene in 15,318 U.S. adults and followed up over an average of 13.9 years to see which of the participants had died as of December 31, 2006.

After controlling for demographic, health and lifestyle factors, the researchers "found that serum alpha-carotene concentration was inversely associated with adjusted risk of death," according to their study, led by Chaoyang Li, of the Office of Surveillance, Epidemiology and Laboratory Services at the Centers for Disease Control and Prevention. Women tended to have slightly higher concentrations of the nutrient than men (5.31 microgram per deciliter versus 4.22).

The team found an especially strong correlation between higher alpha-carotene levels and lower risk of death from diabetes, upper respiratory tract and upper digestive tract cancers, as well as lower respiratory disease.

The findings are slated to be published next year in the March 28 issue of Archives of Internal Medicine and are now available online. A handful of previous, smaller studies of alpha-carotene had mixed results, and the researchers cautioned that the levels of alpha-carotene, rather than having a direct affect on disease prevention themselves might instead "act as an indicator of multiple interactive forces."

Unlike beta-carotene, alpha-carotene is not often found in multivitamins or other common dietary supplements, which suggests that most of the quantities found in people's blood comes from food (primarily yellow-orange and dark green veggies, including broccoli, carrots, collards, green beans, lettuce, peas, pumpkin, spinach, sweet potatoes and winter squash). And a previous case-control study found that eating more of these sorts of alpha-carotene-rich veggies led to a decreased risk of lung cancer.

"These findings support increasing fruit and vegetable consumption as a means of preventing premature death," the researchers noted. So go ahead and raise those carrots high.

Image courtesy of iStockphoto/irabassi