A study of the interactive effects of oral contraceptive use and dietary fat intake on blood pressure, cardiovascular reactivity and glucose tolerance in normotensive women.

ABSTRACT

OBJECTIVE: To investigate the interactive effects of oral contraceptive pill use and dietary fat intake on cardiovascular haemodynamics and metabolic parameters in young normotensive women. DESIGN: Thirty-two women participated, of whom 16 were taking oral contraceptive pills (ethinyl-oestradiol plus levonorgestrel) and 16 were age-matched and weight-matched controls not taking such pills. Subjects consumed either a high-fat or a low-fat diet for 2 weeks in an open, randomized, crossover study lasting 6 weeks. Investigations were performed at the end of each diet during the luteal phase of the menstrual cycle. METHODS: Blood pressure was measured by 24 h ambulatory recording; cardiovascular reactivity was determined by examining blood pressure responses to systemic infusions of noradrenaline and angiotensin II and to the cold pressor test; and carbohydrate metabolism was investigated by an intravenous glucose-tolerance test. RESULTS: Plasma triglyceride levels were significantly higher in women taking oral contraceptive pills compared with non-users on both diets; however, responses of lipoprotein levels to the two diets did not differ between study groups (total and low-density lipoprotein cholesterol levels decreased by 15 and 17% in oral contraceptive pill users and by 14% each in non-users, on the low-fat compared with the high-fat diet). Fasting plasma insulin levels, the insulin-production response to administration of glucose (insulin area under the curve) and resting clinic and night-time systolic blood pressures were all significantly reduced on the low-fat diet, but only in non-users. Blood pressure responses to noradrenaline and maximal heart rate response to cold were significantly attenuated during the low-fat diet in oral contraceptive pill users. During the low-fat diet, resting systolic, 24 h systolic and diastolic blood pressures and insulin area under the curve were all significantly higher for women taking the oral contraceptive pills. Users of these pills also exhibited a greater systolic sensitivity to administration both of noradrenaline and of angiotensin II and had a higher plasma renin activity irrespective of dietary phase. CONCLUSIONS: These results confirm that oral contraceptive pills have the potential to cause adverse effects on blood pressure, cardiovascular reactivity and the insulin-production response to administration of glucose and suggest that some of the beneficial effects of a low-fat diet on these parameters may be negated in women taking oral contraceptive pills.

ABSTRACT

PIP The interactive effects of combined oral contraceptive (OC) use and dietary fat intake on cardiovascular hemodynamics and metabolic parameters were investigated in a comparative study of 16 normotensive OC users from Australia and 16 age- and weight-matched nonuser controls. The 6-week study's crossover design allocated women to consume either a high- or low-fat diet for 2-week periods. Analyses were performed at the end of each diet during the luteal phase of the menstrual cycle. Plasma triglyceride levels were significantly higher in OC users than nonusers in both diet groups; however, responses of lipoprotein levels to the 2 diets did not differ between study groups. Total and low-density lipoprotein cholesterol levels decreased by 15% and 17%, respectively, in OC users, and by 14% each in non-OC users on the low-fat, compared to the high-fat, diet. Fasting plasma insulin levels, the insulin production response to administration of glucose, and resting clinic and night-time systolic blood pressures were all significantly reduced on the low-fat diet, but only in nonusers. In OC users, blood pressure responses to noradrenaline and maximal heart rate response to cold were significantly attenuated by the low-fat diet. During the low-fat diet, resting systolic, 24-hour systolic, and diastolic blood pressures and areas under the curve were significantly higher in the OC group. OC users also demonstrated a greater systolic sensitivity to administration of both noradrenaline and angiotensin II, and had a higher plasma renin activity, regardless of diet. Overall, these findings confirm that OCs can cause adverse effects on blood pressure, cardiovascular reactivity, and the insulin production response to glucose administration, and negate some of the beneficial effects of a low-fat diet.