- Exercise increases B-vitamin (B6, B12, folate) dependent metabolic reactions, especially those related to energy production and the rebuilding and repairing of muscle tissue. These same B-vitamins are also important in maintaining low blood levels of homocysteine (Hcy), a cardiovascular disease (CVD) risk factor. Hcy levels rise when the metabolism of the essential amino acid, methionine increases, a process that requires vitamin B6, B12 and folate. Finally, high intensity exercise can increase methionine metabolism, which can result in elevated Hcy production, particularly if circulating B-vitamins levels are low. Although exercise is a positive modulator of CVD risk, exercise may increase Hcy production and subsequently increase B-vitamin needs, particularly if the exercise intensity is vigorous. Research examining the effect of exercise on Hcy is limited with no studies carefully controlling for factors that alter Hcy metabolism (age, B-vitamins) to determine if Hcy is higher in active than sedentary individuals. Lack of such knowledge limits our ability to make appropriate dietary
recommendations for active individuals. Research on this issue is equivocal due to a variety of study designs and inadequate control of confounding variables. Furthermore, there is much discussion in the B-vitamin/exercise literature about exercise increasing the need for the B-vitamins, but at the moment these data are limited. Therefore, the primary purpose of this research was to examine the effect of physical activity level (HighPA >420 min/wk; LowPA <420 min/wk) on blood Hcy concentrations, independent of B-vitamin status, in non-supplemented young active and sedentary men and women (N=76). A brief introduction (chapter 1) reviews the most recent publications (2005-2007) examining these relationships, research questions, hypotheses, and outcome variables. Then, an extensive review (chapter 2) of Hcy metabolism, blood Hcy as a cardiovascular disease risk factor, and previous publications (1995-2005) on PA and Hcy follows. Finally, chapter 3 describes the study details examining the research questions. Results from this cross-sectional study found no significant differences in blood Hcy concentrations after controlling for plasma B-vitamin levels between HighPA (7.5±1.6 μmol/L) and LowPA (7.7±1.6 μmol/L) groups in young (26±5 y) non-supplemented men (N=38) and women (N=38), unless PA was extremely high (>758 min/wk; >12.5 h/wk).