Confused About Carotenoids?
Friday, June 10, 2016
Epidemiological studies demonstrate that a high dietary intake of specific carotenoids may offer protection against disease, including age-related diseases of the eye, cardiovascular system and brain.
Major carotenoids that have been found in human plasma are divided into two groups: singlet oxygen quenching carotenes (nonpolar molecules, such as β-carotene, α-carotene or lycopene) and xanthophylls (polar carotenoids that include an oxygen atom in their structure, such as lutein, zeaxanthin and β-cryptoxanthin).
Once you understand this simple biochemistry, it may become a bit clearer why the vitamin A-forming nonpolar carotenes, including beta carotene, and the xanthophyll polar carotenoids, lutein and zeaxanthin, might tend to fight for lipoprotein transport space in the human body.
Xanthophylls are suggested to account for about 70 percent of total carotenoids in all brain regions, so it seems reasonable to give xanthophyll carotenoids absorption time before introducing nonpolar carotenes into the diet, since they compete for absorption transport.
Some specific properties of these polar carotenoids must explain why they, among other available carotenoids, were selected during evolution to protect the retina and brain. It is also likely that the selective uptake and deposition of macular xanthophylls in the retina and brain are enhanced by specific xanthophyll-binding lipoproteins.
Some hypothesize that the high membrane solubility and preferential transmembrane orientation of macular xanthophylls distinguish them from other dietary carotenoids, enhance their chemical and physical stability in retina and brain membranes, and maximize their protective action in these tissues.
Most important, xanthophylls are selectively concentrated in the most vulnerable regions of lipid bilayer membranes enriched in polyunsaturated lipids, such as the eye and brain.
This localization is ideal if macular xanthophylls are to act as at-the-ready, lipid-soluble antioxidants, which is the most accepted mechanism through which lutein and zeaxanthin protect neural tissue against degenerative diseases.
According to the esteemed biochemistry professor and much published author John Landrum, PhD, "The transmembrane location of a significant portion of macular xanthophylls in the retinal cells seems obvious. Such a location explains their very slow removal from the retina, which was observed in a study in 1997 that followed the discontinuation of a lutein supplement given to healthy volunteers.
"After stopping a 140-day lutein supplement, our researchers observed a relatively fast decrease in lutein concentration in the serum, whereas the level of lutein in the retina remained unchanged and at a high concentration for up to 6 months.
"These observations suggest that the strong anchoring of xanthophyll molecules at opposite membrane surfaces by polar hydroxyl groups is significant not only in enhancing their effects on membrane properties, but also in the stabilization of these molecules in membranes of the human retina."
Ellen Troyer, with Spencer Thornton, MD, and the Biosyntrx staff
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