Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/1998
Publication Date: N/A
Citation: Interpretive Summary: Selenium (Se) is an essential nutrient, and in the past, it has been thought that the primary purpose of Se in the body was to help important enzymes, such as glutathione peroxidase (GSH-Px), function. These functions of Se can be easily assessed by measuring the amount of Se in a tissue, and by measuring the GSH-Px activity of that tissue. Recent studies have shown that Se has other beneficial qualities, such as protection against cancer and improvement of mood. The way the body uses Se is dependent both on the amount of Se and the chemical form it is present in the diet. For example, Se in garlic is in a variety of forms not normally encountered in meat and bread, the primary sources of Se. Yet garlic has potent anti-cancer properties related to Se. Broccoli contains many of the same forms of Se, so this study was done to compare the efficiency of Se in broccoli to Se in more common forms in its ability to restore Se concentrations and GSH-Px activities in Se-deprived rats. In general, Se from broccoli was not as effective as Se from other sources (Se salts or amino acids) in restoration of these measures. However, the way in which these measures were restored by Se from broccoli suggested that Se was being metabolized in a completely different manner, perhaps in a way in which Se had a function other than being stored in tissues. Future studies should concentrate on developing methods that assess these other beneficial functions of Se, and determine how effective the Se in broccoli is in restoring these functions.
Technical Abstract: A study was conducted to determine the bioavailability of selenium (Se) from broccoli. Ninety-six weanling Sprague Dawley rats (males) were fed a Torula yeast based diet, or a torula yeast based diet with 0.1 mg Se/kg added as selenate (controls) for six weeks. Animals fed the Se deficient diet liver cytosol GSH-Px activities that were 1.3% of controls. Selenium deficient animals were then re-fed diets, for 63 days, that contained 0.1 mg Se/kg diet in which the Se was supplied as either selenate, selenite, selenomethionine (SeMet), or high Se broccoli. High Se broccoli was grown hydroponically and contained 28 mg Se/kg, on a dry weight basis. Absorption of Se from high Se brocolli was significantly lower than from other sources. Selenite, selenate and SeMet were similarly effective in restoring most measures of Se status; broccoli was much less effective. However, selenate, selenite and SeMet began to saturate measures of Se status within 42 days, whereas Se from high Se broccoli caused a linear increase in most measures of Se status throughout 63 days. Selenium from high Se broccoli was as effective as the other forms in restoring kidney and plasma Se concentrations after 63d of feeding. We conclude that Se from broccoli is not as effective as selenite, selenate and SeMet in restoring tissue Se concentrations and GSH-Px activities, but this may be related to Se in broccoli being in a form that is not primarily incorporated in seleno-proteins. Possibly, the form of Se in broccoli is more useful in other functions of Se, such as cancer protection, and thus the method of determining bioavailability of Se by repletion of tissue Se concentrations and GSH-Px activities may not adequately test its bioavailability.