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The influence of breast and bottle feeding on blood pressure
Midwz~Ty(1988)4, 130-132
© Longman Group UK Ltd 1988
Midwifery
The i n f l u e n c e of breast and b o t t l e feeding on blood pressure L. Butters and R. M c C a b e
A prospective study c o m p a r i n g the b l o o d pressure of 21 breast feeding m o t h e r s with 21 m o t h e r s w h o were bottle feeding their b a b y was carried out on the fourth p o s t n a t a l day. T h e a i m of the s t u d y was to establish w h e t h e r breast feeding h a d a n y influence on blood pressure in the i m m e d i a t e p o s t n a t a l period. A l t h o u g h systolic blood pressure tended to be higher in the breast feeding g r o u p the difference did not r e a c h statistical significance. W e c o n c l u d e d that breast feeding has no significant effect on blood pressure in the early p o s t n a t a l days.
INTRODUCTION Hypertension which develops for the first time following delivery is uncommon, occurring 2-3 times per year in this unit with 2300 deliveries. However, when it does occur the hypertension is often severe. We had noticed that, in our small series of women with postnatal hypertension, there was a disproportionate number of women who were breast feeding, This led us to consider whether the physiological changes and practical difficulties associated with different types of feeding affected blood pressure in different ways. We therefore decided to carry out a study to evaluate the influence of breast and bottle feeding on blood pressure. A detailed search of both nursing and medical literature revealed no similar research in this area.
Methods Criteria tbr entry to the study were that subjects Lucy Butters RGN, SCM, Research Midwife. Rosemary McCabe RGN, SCM, Research Midwife. University Department of Materia Medica, Stobhill General Hospital, Glasgow G21 3UW. (Reprint requests to LB) Manuscript accepted 3 May 1988
130
should have had a normal pregnancy followed by a normal delivery, they should have been normotensive throughout pregnancy and at the time of the study. Women ,were recruited from a postnatal ward of this hospital over a period of approximately 1 year. Twenty-one bottle feeding and 21 breast feeding women agreed to participate in the study. There was no difference in age, parity and weight between the breast and bottle feeding women. Blood pressures were measured, on the fourth postnatal day, using a Sentron semi automated sphygmomanometer after 15 minutes rest in the sitting or semi recumbent position on five separate occasions: immediately before commencing feeding, during feeding (once feeding was established), immediately after feeding, 30 minutes after feeding and 60 minutes after feeding. Data are expressed as mean + standard deviation. Blood pressures at 'booking' were compared by unpaired t test. Between group analysis for the study itself was performed by repeated measures analysis of variance (Winer, 1971) using the BMDP statistical package (Dixon, 1977). The values quoted refer to the overall sequential blood pressure means for both groups. The study had a 95% chance of detecting a 15%
MIDWIFERY
150 140 BP 120 (mmHg) 130 110 100 90 80 70 60 50
II
131
-1-
I
BEFORE FEEDING
[]
BREAST FEEDING
O BOTTLE FEEDING
DURING IMMEDIATELY 30MINS FEEDING AFTER AFTER
60MrNS
AFTER
Fig. 1 Blood pressures for breast and bottle feeding women taken on the fourth post natal day. The top of the rectangles refer to systolic blood pressure and the bottom of the rectangles to diastolic blood pressure; shown as means ± standard deviation.
difference between groups at the 5% level of significance (Freiman et al, 1978).
Findings Blood pressure at 'booking" was the same in both groups; systolic blood pressure was 1 1 8 i l l m m H g and 118 4-15 m m H g ( p < 0 . 9 ) while diastolic blood pressure was 74 + 1 l m m H g and 684-13 m m H g ( p < 0 . l) in the breast and bottle feeding groups respectively. Systolic and diastolic blood pressures for breast and bottle feeding during the study period are shown in Figure 1. Systolic blood pressure tended to be higher at all time points in the breast feeding group although the difference just failed to reach statistical significance (p<0.06). There was no significant dit: ference in diastolic blood pressure between the two groups (p < 0.4).
DISCUSSION There are numerous possible environmental and physiological factors which could influence blood pressure in the postnatal period. A study of plasma prolactin and puerperal blood pressure (Jenkins & Soltan, 1980) showed no association between the raised levels of prolactin in breast t~eding women and blood pressure. Interestingly, although the measurements in this study were made at a time remote from feeding, and no statistical analysis was performed, blood pressure appeared to be higher in the breast tEeding group from the first to the fburth postnatal day. Excite-
ment and short term stress cause transient rises in blood pressure and can lead to hypertension being wrongly diagnosed. A study of blood pressure in the puerperium found blood pressure to be slightly higher in primigravida than multipara (Walters et al, 1986), This finding could suggest that stress m a y be responsible for rises in blood pressure in the puerperium. Physical exhaustion, pain and emotional instability after childbirth and the uncertainty experienced under the changing and unpredictable circumstances of short term hospital admission m a y cause transient rises in blood pressure. Although these experiences are common to all women they may be more acute in the primigravida. Systolic blood pressure was consistantly higher in the breast feeding group suggesting that breast feeding itself may be more stressful than bottle feeding in the first week following delivery. Worries about how much milk the baby is getting and whether it is getting enough, lack of sleep, sore nipples, and a reluctance to take analgesics could all contribute to the increased systolic blood pressures in the breast feeding women. The differences in systolic blood pressure between breast and bottle feeding women which we observed in this study are unlikely to present diagnostic difficulties in differentiating normotensive fiom hypertensive women.
Acknowledgements Lucy Butters is supported by the Wellcorne Trust. Rosemary McCabe was supported by the Scottish Home and Health Department.
132
MIDWIFERY
References Dixon WJ (ed) 1977 Biomedical Computing Programs, P series. Berkley, University of California Press Jenkins D M, Soltan M M 1980 Plasma prolactin and puerperal blood pressure. British Journal of Obstetrics and Gynaecology 87:597-599 Freiman J A, Chalmers T C, Smith H 1978 The importance
ofbeta~ the type 1I error and sample size in the design and interpretation of the randomized control trial. New England Journal of Medicine 299:690 694 Walters B N J, Thompson M E, Lee A, De Swiet N 1986 Blood pressure in the puerperium. Clinical Science 71 : 589-594 Winer BJ 1971 Statistical principles in experimental design. 2nd Ed. New York, McGraw-Hill
© Longman Group UK Ltd 1988
Midwifery
The i n f l u e n c e of breast and b o t t l e feeding on blood pressure L. Butters and R. M c C a b e
A prospective study c o m p a r i n g the b l o o d pressure of 21 breast feeding m o t h e r s with 21 m o t h e r s w h o were bottle feeding their b a b y was carried out on the fourth p o s t n a t a l day. T h e a i m of the s t u d y was to establish w h e t h e r breast feeding h a d a n y influence on blood pressure in the i m m e d i a t e p o s t n a t a l period. A l t h o u g h systolic blood pressure tended to be higher in the breast feeding g r o u p the difference did not r e a c h statistical significance. W e c o n c l u d e d that breast feeding has no significant effect on blood pressure in the early p o s t n a t a l days.
INTRODUCTION Hypertension which develops for the first time following delivery is uncommon, occurring 2-3 times per year in this unit with 2300 deliveries. However, when it does occur the hypertension is often severe. We had noticed that, in our small series of women with postnatal hypertension, there was a disproportionate number of women who were breast feeding, This led us to consider whether the physiological changes and practical difficulties associated with different types of feeding affected blood pressure in different ways. We therefore decided to carry out a study to evaluate the influence of breast and bottle feeding on blood pressure. A detailed search of both nursing and medical literature revealed no similar research in this area.
Methods Criteria tbr entry to the study were that subjects Lucy Butters RGN, SCM, Research Midwife. Rosemary McCabe RGN, SCM, Research Midwife. University Department of Materia Medica, Stobhill General Hospital, Glasgow G21 3UW. (Reprint requests to LB) Manuscript accepted 3 May 1988
130
should have had a normal pregnancy followed by a normal delivery, they should have been normotensive throughout pregnancy and at the time of the study. Women ,were recruited from a postnatal ward of this hospital over a period of approximately 1 year. Twenty-one bottle feeding and 21 breast feeding women agreed to participate in the study. There was no difference in age, parity and weight between the breast and bottle feeding women. Blood pressures were measured, on the fourth postnatal day, using a Sentron semi automated sphygmomanometer after 15 minutes rest in the sitting or semi recumbent position on five separate occasions: immediately before commencing feeding, during feeding (once feeding was established), immediately after feeding, 30 minutes after feeding and 60 minutes after feeding. Data are expressed as mean + standard deviation. Blood pressures at 'booking' were compared by unpaired t test. Between group analysis for the study itself was performed by repeated measures analysis of variance (Winer, 1971) using the BMDP statistical package (Dixon, 1977). The values quoted refer to the overall sequential blood pressure means for both groups. The study had a 95% chance of detecting a 15%
MIDWIFERY
150 140 BP 120 (mmHg) 130 110 100 90 80 70 60 50
II
131
-1-
I
BEFORE FEEDING
[]
BREAST FEEDING
O BOTTLE FEEDING
DURING IMMEDIATELY 30MINS FEEDING AFTER AFTER
60MrNS
AFTER
Fig. 1 Blood pressures for breast and bottle feeding women taken on the fourth post natal day. The top of the rectangles refer to systolic blood pressure and the bottom of the rectangles to diastolic blood pressure; shown as means ± standard deviation.
difference between groups at the 5% level of significance (Freiman et al, 1978).
Findings Blood pressure at 'booking" was the same in both groups; systolic blood pressure was 1 1 8 i l l m m H g and 118 4-15 m m H g ( p < 0 . 9 ) while diastolic blood pressure was 74 + 1 l m m H g and 684-13 m m H g ( p < 0 . l) in the breast and bottle feeding groups respectively. Systolic and diastolic blood pressures for breast and bottle feeding during the study period are shown in Figure 1. Systolic blood pressure tended to be higher at all time points in the breast feeding group although the difference just failed to reach statistical significance (p<0.06). There was no significant dit: ference in diastolic blood pressure between the two groups (p < 0.4).
DISCUSSION There are numerous possible environmental and physiological factors which could influence blood pressure in the postnatal period. A study of plasma prolactin and puerperal blood pressure (Jenkins & Soltan, 1980) showed no association between the raised levels of prolactin in breast t~eding women and blood pressure. Interestingly, although the measurements in this study were made at a time remote from feeding, and no statistical analysis was performed, blood pressure appeared to be higher in the breast tEeding group from the first to the fburth postnatal day. Excite-
ment and short term stress cause transient rises in blood pressure and can lead to hypertension being wrongly diagnosed. A study of blood pressure in the puerperium found blood pressure to be slightly higher in primigravida than multipara (Walters et al, 1986), This finding could suggest that stress m a y be responsible for rises in blood pressure in the puerperium. Physical exhaustion, pain and emotional instability after childbirth and the uncertainty experienced under the changing and unpredictable circumstances of short term hospital admission m a y cause transient rises in blood pressure. Although these experiences are common to all women they may be more acute in the primigravida. Systolic blood pressure was consistantly higher in the breast feeding group suggesting that breast feeding itself may be more stressful than bottle feeding in the first week following delivery. Worries about how much milk the baby is getting and whether it is getting enough, lack of sleep, sore nipples, and a reluctance to take analgesics could all contribute to the increased systolic blood pressures in the breast feeding women. The differences in systolic blood pressure between breast and bottle feeding women which we observed in this study are unlikely to present diagnostic difficulties in differentiating normotensive fiom hypertensive women.
Acknowledgements Lucy Butters is supported by the Wellcorne Trust. Rosemary McCabe was supported by the Scottish Home and Health Department.
132
MIDWIFERY
References Dixon WJ (ed) 1977 Biomedical Computing Programs, P series. Berkley, University of California Press Jenkins D M, Soltan M M 1980 Plasma prolactin and puerperal blood pressure. British Journal of Obstetrics and Gynaecology 87:597-599 Freiman J A, Chalmers T C, Smith H 1978 The importance
ofbeta~ the type 1I error and sample size in the design and interpretation of the randomized control trial. New England Journal of Medicine 299:690 694 Walters B N J, Thompson M E, Lee A, De Swiet N 1986 Blood pressure in the puerperium. Clinical Science 71 : 589-594 Winer BJ 1971 Statistical principles in experimental design. 2nd Ed. New York, McGraw-Hill