It has been reported that TC, LDLC and TG concentrations increase from
30–35-year-olds to 50–60-year-olds, and the serum lipid profile becomes almost constant after then in women [20
]. The rises have been reported to be 20–30 mg/dl in TC, 30–40 mg/dl in LDLC and 35–40 mg/dl in TG [20
]. Especially, TC and LDLC concentrations remarkably increase between 4 years before and 1 year after menopause [22
], and there is a large difference between premenopausal and postmenopausal women [23
]. HDLC concentration decreases a little with aging from age 20 [20
], and the characteristic change around menopause is not observed. In this study, all subjects were around menopausal age; in fact, six subjects changed to postmenopausal from menopausal status and five subjects changed to menopausal from premenopausal status during the course of the study: Taking the age and the menstruation status into consideration, the subjects were put in the stage in which serum lipids were most easy to deteriorate. It is a primary goal to stop the deterioration of the lipids in women in this particular stage. Our results showed that HDLC and TC : HDLC ratio were significantly improved in the exercise group. HDLC after 24 months in the exercise group was higher compared with the control group. Regarding TC: HDLC ratio after 24 months, the obtained values in the exercise group were significantly lower than that in the control group. It is evident from these that exercise stops the deterioration of the lipid profile in women around menopause. There are some reports with results similar to ours [5
]. It is possible to assume that a woman close to menopausal age would not obstruct the improvement of serum lipids through exercise. Moreover, the results obtained showed that the most influential factor was each initial value marking the improvement of TC: HDLC ratio and LPO; there are similar reports by others [6
]. Consequently, we arrive at the conclusion that exercise is very useful for women around menopause not only to prevent the value from deteriorating but also to return the levels that have already deteriorated.
Consider now the factors related to the improvement of the serum lipids. The postmenopausal state affected the values of HDLC and TC: HDLC ratio. This fact is known as the effect of estrogen decrease. It was shown that the values of TC, HDLC and TC: HDLC ratio were related to the number of daily steps, which in turn affected the changes of TC and HDLC for 24 months. These results demonstrate that increasing of the number of daily steps work improves or at least maintains a good levels of the serum lipids. Irie et al.
] reported that an increased number of steps was significantly correlated with increased HDLC, and this fact supports our view. In our study, the average of the number of steps per day for the first week was about 6,500. This is almost the same as the average of the number of daily steps in Japanese homemakers [34
], and it reflects the lifestyle of those who do not move very much. By encouraging the increase in the number of daily steps taken, our subjects increased them to about 9,000. Duncan et al
] found that HDLC concentration and TC : HDLC ratio improved not in their aerobic group or brisk group, but in their strolling group. Reaven et al.
] also noted that HDLC concentrations were the highest in the group in which the physical activity level was light. It is reasonable to suppose that the improvement can be expected even in exercise of low intensity. In the view of Blair et al.
], the response to exercise depends on neither the intensity nor the length of the training period, duration of exercise session, or the frequency, etc. When considering the exercise conditions applied until now by research on women, the frequency was mostly 3–5 times/week and the duration of an exercise session was 20–60 minutes. There is a difference between longitudinal research and cross-sectional research in the training period; it is between 10 weeks and 12 months and between 3 years and 5 years, respectively. The effect of exercise on the lipids is different among various studies conducted in longitudinal research. On the other hand, the value of lipids in trained women is obviously better than in untrained women in cross-sectional research. This fact indicates that the lipids are surely improved owing to long-term exercise. In our study, it seems that suitable results were obtained because the period of exercise was long, though the intensity of exercise was low.
Although the physiological mechanisms that involved in the decrease of TC and the increase of HDLC due to low intensity physical activity were not directly examined in the present study, several possible mechanisms have been proposed to explain them. Some investigators have demonstrated that aerobic exercise increases both plasma lipoprotein lipase and lecithin cholesterol acyltransferase activities [38
]. It would be expected that the same mechanisms might also been presented in the menopausal women. To clarify the related mechanisms, more investigations need to be carried out.
Turn now to the role of the antioxidation that estrogen and LPO had. LPO oxidized the low-density lipoproteins (LDL), and the oxidation of LDL is incorporated by macrophages, becomes a foam cell, and then it becomes deposited in the arterial vessel wall. It is said that it worsens arteriosclerosis, and it is considered in the meantime that estrogen suppresses the LPO. Since estrogen is failing around menopause, it appears that LPO increases. It is necessary to control the increase of LPO and LDL, and toward this end, exercise is expected to play an important role. There is a report on the effect of exercise on the oxidation of LDL, whose production could be suppressed by 10-month exercise [40
]. There is no other survey examining on the effect of long-term exercise. In many surveys, it was found that acute exercise accelerated the generation of LPO [41
]. In this study, LPO concentration decreased, though not significantly, and the factor that affected the alteration of LPO could not be clarified by multiple regression analysis. In the future, it will be necessary to sufficiently examine the effect of long-term exercise on the generation of LPO and oxygen action including the effects of menstruation.
In follow-up studies involving physical education class, the number of persons who participate throughout the entire term of investigation is an important factor. Participation rate of about 60% has been reported [43
]. In the current study, moderate exercise regimen had a practice rate 62.5% for 24 months. Thus, we can speculate that moderate exercise, as applied in our study, may improve the practice rate.
We have undertaken another study a large number of controls and exercise group. Our goal is to overcome a number of weakness points we have been facing in the present investigation including: small subjects' numbers and lack of dietary control. In addition, it would have been desirable to perform analyses by dividing the subjects into the same status of menopause. However, in the present study the number of subjects was not enough to do so. The results of upcoming research would further our understanding of the effects of moderate exercise and serum lipids status in women.