This chapter will focus on the potential roles of fat-soluble nutrients and fat-soluble antioxidants in preventing cardiovascular disease (CVD). Two fat-soluble vitamins will be discussed in detail, i.e. vitamin E and vitamin D. Vitamin E (tocopherols and tocotrienols) is generally considered an antioxidant nutrient, although it may have important functions unrelated to its antioxidant functions (as discussed below). Antioxidant nutrients function by preventing damage to biological systems caused by reactive oxygen species (ROS) and/or reactive nitrogen oxide species (RNOS). Vitamin D (calciferols) is not a true vitamin since it is not required in our diet, can be produced in skin tissue, and is generally not present in plants. Vitamin D is, perhaps, best described as a steroid hormone precursor. Although vitamin D may function as a membrane antioxidant under in vitro conditions (Wiseman, 1993), its primary biological role is to maintain plasma calcium and phosphorus homeostasis.
The additional fat-soluble antioxidant nutrient reviewed here will be coenzyme Q10 (ubiquinone or CoQIO), which has strong antioxidant properties. Vitamin E and CoQIO can protect lipid-protein complexes, such as biological membranes and lipoproteins, from lipid peroxidation. During lipid peroxidation, highly reactive lipid hydroperoxides, peroxyl radicals and reactive aldehydes, such as malondialdehyde (MDA) and 4-hydroxynonenol (4-HNE), are generated. The peroxyl radicals support chain reactions that can rapidly damage oils, biological membranes or lipoproteins containing polyunsaturated fatty acids (PUFA).
The literature reviewed below strongly suggests that oxidative stress plays a key role in the etiology of cardiovascular disease. Oxidative stress is a physiological condition in which pro-oxidant factors outweigh antioxidant defences. Accordingly, the role of oxidative stress in promoting cardiovascular disease and the roles of fat-soluble antioxidant nutrients in potentially protecting from this disease process will be discussed in some detail. Oxidative stress is likely to occur during inflammatory processes, during exercise and from cigarette smoking. The evidence presented below also suggests that vitamin D plays an important and significant role in preventing cardiovascular disease but it is very unlikely that this effect is related to its potential role as an antioxidant.
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