A debate has been raging concerning the role of carotenoids and heart health with various intervention trials reporting that supplementation with beta-carotene failed to have the effects suggested by epidemiological studies.
These disappointments, suggest the researchers from the University Hospital in Linkoping, may be due to the lack of focus on other carotenoids, such as lutein and zeaxanthin, with several studies already reporting positive links between lutein consumption and heart health (for example: Circulation, 2001, Vol.103, pp. 2922-2927).
"To the best of our knowledge, the present study is the first to have investigated the plasma levels of oxygenated and hydrocarbon carotenoids in CAD patients," wrote lead author Caroline Lidbjer in the journal Nutrition, Metabolism and Cardiovascular Diseases (doi: 10.1016/j.numecd.2006.02.006).
Alpha- and beta-carotene, as well as lycopene, are so-called hydrocarbon carotenoids, meaning they contain only hydrogen and carbon atoms, while lutein, zeaxanthin and beta-cryptoxanthin are oxygenated carotenoids, meaning they contain oxygen atoms in addition to the hydrocarbon skeleton.
The new study recruited 89 patients with CAD (50 with stable angina, 39 with acute coronary syndrome), as well as 50 healthy control subjects. The researchers used high-performance liquid chromatography (HPLC) to measure plasma carotenoid levels from blood samples.
Interestingly, the researchers found that the healthy controls had significantly higher plasma levels of lutein plus zeaxanthin (037 micromoles per litre) and beta-cryptoxanthin (0.17 micromoles per litre) than the CAD patients (0.27 and 0.10 micromoles per litre, respectively). There were no significant differences between controls and CAD patients for the other hydrocarbon carotenoids studied.
Lower levels of the oxygenated carotenoids was also linked to smoking, higher BMI, and lower HDL-cholesterol levels. However, when the researchers accounted for these other factors, there was still a significant link between lutein, zeaxanthin and beta-cryptoxanthin levels and artery health.
"The measure of oxygenated carotenoids in plasma might therefore be a useful tool to identify candidates who are potential responders to antioxidant [supplementation]," wrote the researchers.
In other words, the results of this study suggest that higher levels of these carotenoids may be linked to improved cardiovascular health, which is in-line with the findings from the Los Angeles atherosclerosis study (Circulation, 2001, Vol.103, pp. 2922-2927).
It was also found that lutein and zeaxanthin levels were also associated with levels of the natural killer cells (NK cells), cells that form a major component of the human immune response system.
"This finding suggests a specific link between certain carotenoids, oxidative stress and immune perturbation in CAD," said Lidebjer. "NK cells have been shown to be particularly sensitive to oxidative stress."
The mechanism behind potential protective effects of the carotenoids follows this link: The antioxidants reduce the oxidative stress in the body, and therefore benefit NK cell numbers which can then aid the inane immune system response of the individual.
This preliminary proposal of the mechanism and the link between oxygenated carotenoids and immune system function "calls for further investigation".
This study is sure to re-ignite the debate between these carotenoids and heart health, after a study from Harvard last year came to the conclusion that intake of lutein and zeaxanthin might increase the risk of a heart attack (Journal of Nutrition, 2005, Vol. 135, pp. 1763-1769).
Dietary sources of lutein and zeaxanthin include corn, egg yolk, broccoli, green beans, cabbage, lettuce and kiwi fruit.