November 26, 2010

Longer life associated with higher alpha-carotene levels

An article appearing online on November 22, 2010 in the American Medical Association journal Archives of Internal Medicine reports the discovery by researchers at the Centers for Disease Control and Prevention in Atlanta of an association between higher serum levels of the carotenoid alpha-carotene and a lower risk of dying over a 13.9 year average period.

Chaoyang Li, MD, PhD and colleagues evaluated data from 15,318 adults who enrolled in the Third National Health and Nutrition Examination Survey Follow-up Study between 1988 and 1994. Blood samples drawn upon enrollment were analyzed for serum alpha-carotene and other factors. The participants were followed through 2006 during which the causes of deaths that occurred were recorded.

Over the follow-up period, there were 3,810 deaths, including 1,671 from cardiovascular disease and 834 from cancer. As serum alpha-carotene levels increased there was a corresponding decline in the risk of dying. Among participants whose alpha-carotene levels were highest at 9 or more micrograms per deciliter, there was a 39 percent lower adjusted risk of dying from any cause compared with those whose levels were lowest at 0 to 1 mcg/dL. When deaths were examined by cause, those whose alpha-carotene levels were highest had a 29 percent lower risk of dying from cardiovascular disease, a 43 percent lower risk of cancer mortality, and a 45 percent lower risk of dying from other causes in comparison with the lowest group. The inverse association was independent of demographic characteristics, lifestyle and traditional health risk factors.

In their introduction to the article, Drs Li and associates note that oxidative damage to DNA, proteins and lipids may play a role in the development of cancer, cardiovascular disease and other chronic diseases. Carotenoids such as alpha-carotene scavenge reactive oxygen and nitrogen species, thereby helping to prevent oxidative damage. "Although alpha-carotene is chemically similar to beta-carotene, in vivo study results suggest that alpha-carotene is about 10 times more effective than beta-carotene in inhibiting the proliferation of human neuroblastoma cells; that alpha-carotene, but not beta-carotene, has a potent inhibitory effect against liver carcinogenesis; and that alpha-carotene is more effective than beta-carotene in inhibiting the tumor-promoting action of glycerol in lung carcinogenesis and skin tumor promotion," the authors write. "Moreover, results from a population-based case-control study of the association between the consumption of fruits and vegetables and risk of lung cancer suggest that consumption of yellow-orange (carrots, sweet potatoes or pumpkin and winter squash) and dark-green (broccoli, green beans, green peas, spinach, turnips greens, collards and leaf lettuce) vegetables, which have a high alpha-carotene content, was more strongly associated with a decreased risk of lung cancer than was consumption of all other types of vegetables."

"These findings support increasing fruit and vegetable consumption as a means of preventing premature death," they conclude.

Pancreatic cancer

While the exact cause of pancreatic cancer is not known with certainty, several factors—including smoking, nutrition, glucose levels, hormones, and genetics—are thought to be involved in its initiation and development.

Smoking is a major risk factor, accounting for 25-30 percent of all cases. Heavy smokers are two to three times more at risk for cancer than are nonsmokers (Lowenfels AB et al 2002). Several studies have observed a reduction in pancreatic cancer risk within a decade after smoking cessation (Michaud DS 2004).

DNA damage caused by exposure to free radicals has been found in human pancreatic tissues (Uden S et al 1992). In pancreatic cancer cells, antioxidant levels are much lower compared to those in noncancerous pancreatic cells. Nutritional supplements such as alpha-tocopherol (Ferreira PR et al 2004; Hernaandez J et al 2005; Rautalahti MT et al 1999), ascorbic acid (Zullo A et al 2000), zinc (Ertekin MV et al 2004; Prasad AS et al 2004; Uden S et al 1992), and selenium may be beneficial in elevating antioxidant levels (Zhan CD et al 2004).

Evidence suggests that the increased incidence of pancreatic cancer in Western nations may be related to the relatively low dietary content and qualities of naturally occurring plant hormones (phytoestrogens) (Stephens FO 1999). Daidzein, a phytoestrogen found in soybeans, chickpeas, and dietary supplements, has been shown to slow the growth of pancreatic cell lines (Guo JM et al 2004).

Maintaining adequate blood folate levels or increasing folate intake from dietary or vitamin sources may reduce pancreatic cancer risk significantly (Kim YI 1999). In a study of 27,101 healthy male smokers, 157 developed pancreatic cancer during 13 years of follow-up. Those with the lowest folate intake showed a 48 percent increased risk of pancreatic cancer (Stolzenberg-Solomon RZ et al 2001).

Data support an association between reduced lycopene levels and pancreatic cancer (Comstock GW et al 1991). In a clinical study, low levels of lycopene, retinol, and beta-carotene were strongly associated with pancreatic cancer (Abiaka CD et al 2001). Tomatoes are a rich dietary source of lycopene, which is also available as a dietary supplement (Ansari MS et al 2004).

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