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Flavonoids are a group of naturally occurring antioxidants, which over the past years have gained tremendous interest because of their possible therapeutic applicability. The mechanism of their antioxidant activity has been extensively studied over several decades. However, there is still much confusion about the molecular mechanism of radical scavenging and the relationship between structure and activity. Therefore, we have calculated the heat of formation and the geometry of both the parent compound and the corresponding radical using the ab initio program GAMESS. We have compared their differences in energy in order to gain insight into the stability of the radical and the ease with which it is formed. We have also investigated the spin density of the radical, to determine the delocalization possibilities. These calculated data were compared with experimental data from ESR (hyperfine coupling constants) and electrochemical oxidation (Ep/2) and were found to be in good agreement. By comparing the geometries of several flavonoids, we were able to explain the structural dependency of the antioxidant action of these compounds. The extremely good antioxidant activity of the flavonols could be explained by the formation of an intramolecular hydrogen bond.

Vitamin D deficiency is common in the elderly and may lead to secondary hyperparathyroidism, cortical bone loss, and hip fractures. The effect of vitamin D supplementation for 1 yr was studied in 72 people living in a nursing home and 70 people living in an aged people's home. The subjects were randomized into 3 groups: control, and 400 or 800 IU vitamin D3/day. The initial vitamin D status of each subject was classified as deficient or borderline [serum 25-hydroxyvitamin D (25OHD) less than 30 nmol/L] in 79% and adequate (serum 25OHD greater than or equal to 30 nmol/L) in 21%. Serum 25OHD concentrations increased about 3-fold in both groups receiving vitamin D supplementation. Serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] concentrations increased slightly but significantly, and the increase was inversely related to the initial serum 25OHD concentration. Serum intact PTH-(1-84) concentrations decreased about 15% during supplementation in both nursing home and aged people's home residents, whereas serum osteocalcin significantly decreased in the nursing home residents only. We conclude that a vitamin D3 supplement of 400 IU/day adequately improves vitamin D status in elderly people and increases 1,25-(OH)2D concentrations in those with vitamin D deficiency. Supplementation decreases parathyroid function and may depress bone turnover to some degree.

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Endogenous antioxidants such as the lipid-soluble vitamin E protect the cell membranes from oxidative damage.