Age, sex, cigarette smoking and indices of free radical activity in healthy humans.

OBJECTIVES: To determine the effect of age, sex and smoking on free radical (FR) indices. There is currently considerable research interest into the role of FRs in the pathogenesis of many diseases and it is therefore important to identify factors in healthy subjects which influence the markers used to assess FR activity.
METHODS: Blood samples were obtained from 123 healthy subjects whose age, sex and smoking habits were recorded. The following were measured on each sample: malondialdehyde (MDA) which is a product of FR mediated lipid peroxidation and the FR scavengers plasma thiols (PSH), red cell glutathione (GSH) and superoxide dismutase (SOD).
RESULTS: Malondialdehyde levels were significantly increased in cigarette smokers (p < 0.02) but no significant age related increase in MDA was detected for the group as a whole. However, female smokers had the highest rate of MDA increase with age followed by male smokers and female non-smokers. MDA levels of male non-smokers were unaffected by age. A significant negative correlation was detected between PSH and age (p < 0.001). GSH was significantly higher in females (p < 0.05) and the red cell content of GSH and SOD were significantly inversely related (p < 0.01).
CONCLUSION: This study of normal subjects describes an age related increase in malondialdehyde levels, the rate of which is influenced by sex and smoking status. In humans, plasma thiol levels decrease with increasing age, females have higher red cell glutathione and there is a significant inverse relationship between red blood cell superoxide dismutase and glutathione levels. Furthermore, cigarette smoking increases plasma malondialdehyde levels. With the considerable current interest in free radicals, it is important to identify factors which influence the indices used to assess free radical activity in disease states.