The effects of fluctuations in oestrogen and progesterone during the menstrual cycle on glucose homeostasis, energy balance, exercise and premenstrual syndrome
It is widely accepted that the loss of sex hormones after the menopause is strongly linked with cancer, insulin resistance and obesity, with variations in sex hormone concentrations being responsible in part, for the differences reported in energy metabolism and glycaemic control between genders. As such a greater understanding of the effects that oestrogen and progesterone may have on women's health and their potential long term consequences is required. This thesis reports evidence of three studies investigating the effects of oestrogen and progesterone during the menstrual cycle on glucose and insulin response, energy expenditure, substrate oxidation and premenstrual syndrome (PMS). The aim of the first study was to investigate glucose and insulin responses to a 75g glucose load during different phases of the menstrual cycle. Venous blood samples for baseline measurements of oestradiol and progesterone were collected every other week day from eighteen regularly menstruating women for one complete menstrul cycle. An oral glucose tolerance test (OGIT, 75g glucose) was performed on three separate days during the next complete menstrual cycle. The results report an increase in glucose area under the curve (AUC) and insulin AUC during the luteal phase (P<0.05) compared to the menstrual and follicular phase, but no significant differences in insulin sensitivity between phases. The findings indicate that both oestrogen and progesterone during the luteal phase may affect glycaemic response and this potentially has significant implications for the development of type 2 diabetes over prolonged periods of time. The second study investigated energy expenditure and substrate oxidation at rest and during a 30 minute moderate intensity walking exercise within the three phases of the menstrual cycle. Sex hormone concentrations were collected in the same manner as study 1. Nineteen women undertook resting measures and ten for exercise. The study reports a decrease in carbohydrate (CHO) oxidation (P<0.05) and a marginal increase in fat oxidation (P=0.06) during the follicular phase at rest, with no difference in energy expenditure at rest. No difference in energy expenditure or substrate oxidation between phases was reported during exercise. The results indicate high oestrogen concentrations during the follicular phase only may mediate the changes in substrate oxidation response reported at rest. I The final study investigated the effects of a 12 week moderate intensity exercise intervention on symptoms of PMS, quality of life and dietary intake and determined whether any such effect was associated with changes in oestrogen and progesterone concentrations in a randomised control trial. Twenty-five sedentary women, identified as suffering from PMS symptoms, were recruited to the trial spanning four menstrual cycles, the first serving as a baseline followed by three cycles of intervention. Participants were randomly assigned to either an exercise (EX) group (n= l 3), which involved three supervised 30-minute moderate­ intensity (70-80% HR max) treadmill walking exercise sessions per week, or to a control (CON) group (n=12), which involved attending a 90-minute, one-to-one meeting once per week with the investigator. The results report a reduction in PMS symptoms following the exercise intervention (P<0.05), with no differences in the control (CON) group. Averaged dietary intake over the three intervention cycles reports a decrease in CHO intake (% total energy intake, TEI) during the luteal phase, compared to the menstrual (45.5% vs. 50. l%) and follicular (45.5 vs. 49.9%) phases in the EX group, with no difference in the CON group. No significant difference was reported in overall energy intake in either group. In addition, no significant difference was reported in plasma oestrogen and progesterone concentrations over the four cycles in either group (EX and CON). The findings indicate that the exercise regime reduces PMS symptoms and CHO intake (%TEI), but that these are not mediated in response to changes in oestrogen and progesterone hormone concentrations. As such exercise may therefore be an effective symptom management tool for women suffering with PMS. Further studies are essential to determine the exact duration and intensity required for the most effective symptom relief. The results reported in this thesis provide evidence that the circulating reproductive hormones oestrogen and progesterone during the menstrual cycle have significant implications for energy regulation, glycaemic control and women suffering from PMS. As such, both hormones need to be investigated further in larger research studies to determine their potential long-term adverse effects on health and well-being in women.
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