The following article on

The following article on ‘The Effect of Exercise During Lactation on short- and Long-term Immune Status’ by Laurie Nommsen-Rivers MS, RD IBCLC was originally published in the Journal of Human Lactation and was submitted by Elizabeth Mayo, who is an Infant Feeding Advisor with Cheltenham Hospital and NCT Breastfeeding Counsellor. It helps to answer a commonly asked question. Does exercise adversely affect breastfeeding?

After recovering from childbirth, many new mothers are motivated to “get back in shape” through dieting and/or exercise. However, some women worry that regular exercise is not compatible with lactation. Some of this concern may stem from a well-publicized study showing a decline in the concentration of immune factors in breast milk within the first 30 minutes of a bout of maximal exercise (1). While the results of 2 previously published randomised trials show that breast milk volume and calorie content, in addition to the lipid, protein and lactose concentrations, are not affected by either an intense, short-term (11 days) aerobic exercise program (2) or a more moderate, sustained (10 weeks) regimen (3), neither of these 2 studies measured the effects of exercise on immune factors in breast milk. The anti-infective properties of human milk confer powerful immunity to the breastfed infant. It is understandable that mothers would not want to jeopardize this important benefit of breastfeeding.

Exercise scientists have described the relationship between exercise intensity and immune status as an “inverted J”. In other words, it has generally been observed that as the amount of exercise increases, immune function is enhanced, up to exhaustive levels of exercise (such as running a marathon), which suppresses immune function. Based on the inverted J hypothesis, Lovelady and co-authors theorized that even though Gregory at al found a short-term decline in milk SigA following a test session of exercising to exhaustion (VO2 max test) (1), more realistic levels of exercise would not affect the immune status of lactating mothers or cause a decrease in the levels of immune factors in their breast milk.

To test this hypothesis, Lovelady et al recruited exercising and sedentary mothers of exclusively breastfed 12 plus or minus 2-weeks-old infants to participate in a cross-sectional study of exercise and immune status. A sub-sample of the exercising group also participated in a randomized crossover study of the short-term effects of moderate exercise on immune status. In the first study, the immune status and breast milk composition of 29 lactating women who exercised at least 30 min/d for a minimum of 3 d/wk were compared to that of 24 lactating women who were sedentary (exercised less than 1 d/wk). On the day of laboratory measurements, subjects expressed 30 ml of breast milk during the first morning feed. Study subjects then came into the lab to have a fasting morning blood sample drawn while at rest, followed by a treadmill test.

Although the exercise group showed significantly better cardio respiratory fitness, confirming their regular exercise status, no differences between the exercising and sedentary groups were found in any of the immune factors measured.

Maternal immune status – whether expressed as percentage of absolute counts of Blood T cells, cytotoxic cells, helper T cells, B cells and natural killer cells; leukocytes; lymphocytes; monocytes; neutrophils; haemoglobins or hematocrit – was not significantly different between the groups. Furthermore, breast milk concentrations of secretory IgA, lactoferrin and lysozyme were not significantly different between the exercise and sedentary groups. These results suggest that moderate, regular exercise does not cause long-term alternations in maternal immune status or milk composition.

In the second study, a sub-sample of the regular exercisers (n=17) returned to the lab on 2 separate occasions to have their breast milk sampled before and 10 and 60 minutes after either a 30-minute test session of exercise or rest. The order of the sessions (exercise or rest) was randomly determined for each mother. Unlike the Gregory study, mothers were not exercised to exhaustion. Instead, mothers walked or jogged on the treadmill at a pace that elicited an intensity of approximately 75% of predicted maximum heart rate.

Researchers found no significant difference in breast milk SigA, lactoferrin or lysozyme concentrations between rest and exercise sessions at any of the time points studied (1, 10 and 60 minutes postsession). The only significant comparison was in breast milk lysozyme, which declined significantly over time (from 1 to 10 to 60 minutes post-session), but the degree of decline was similar during both rest and exercise, perhaps reflecting changes in milk composition related to a great degree of breast emptying with each subsequent milk sample.

The combined evidence from these studies provides support for the compatibility of exercise during lactation. Moderate levels of exercise do not appear to have a short- or long-term detrimental effect on the levels of the major immune factors in breast milk. Thus, lactating mothers can be assured that by exercising regularly and continuing to breastfeed, they are providing both themselves and their babies with health benefits.

This article was originally printed in the Journal of Human Lactation 20(4), 2004