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Female participation in sport is growing, including at the elite level. The Tokyo 2020 Olympic Games saw the most gender-equal athlete pool in Summer Olympic Games history along with a female athlete-led campaign to prevent the separation of a lactating athlete from her infant.1 Despite growing numbers of females participating in exercise and sport during pregnancy, there is very little evidence to guide the return to sport following childbirth, and even less evidence on the relationships between lactation and sport participation and performance.2 Exercise has been shown to be compatible with lactation and does not negatively influence milk production or nutritional quality.2 However, elite athletes have reported several barriers to training and competing while lactating, including (1) lack of access to lactation consultants, (2) lack of knowledge among healthcare providers on guiding lactation while meeting the training requirements of an elite athlete and (3) fear of sustaining a bone stress injury (BSI) while lactating.3
The unique physiological status of a lactating female athlete combined with the relative lack of evidence on postpartum exercise poses a clinical challenge to healthcare providers working with these athletes. Several factors, such as changes in endocrine function and increased caloric needs, may influence a lactating athlete’s risk of developing Relative Energy Deficiency in Sport (REDs). It is also possible, though not well studied, that exposure to problematic low energy availability (LEA) and REDs may also negatively influence lactation.3 This editorial highlights some biopsychosocial considerations regarding lactation and REDs and identifies areas for future research to prevent health complications in lactating athletes.
Biopsychosocial overlap of lactation and REDs
Several diagnostic factors have been associated with REDs that may be confounded by lactation. As such, it is imperative that thorough screening and analysis of possible contributing causes be performed when working with a lactating athlete. These factors include, but are not limited to, the following4:
Dietary restriction/drive for thinness/large changes in body weight or composition in a short time period: many postpartum females do not meet recommended energy, vitamin and mineral intake.5 Desire to rapidly return to prepregnancy weight status has been identified in postpartum females, sometimes leading to calorie restriction, dieting or excessive exercise.5 In addition, while symptoms of disordered eating tend to decrease during pregnancy, the risk of a relapse of disordered eating during the postpartum period is very high, and symptoms may be more severe than prepregnancy symptoms.6 These factors can not only adversely impact breastmilk but also increase REDs risk.
Sleep disturbances: decreased energy levels and sleep disturbances are frequently reported after childbirth, particularly in females with postpartum depression.2 Further evaluation of the lactating female athlete to determine whether impaired sleep is due to REDs, sleep disruptions and/or mental health concerns is essential. Research is also needed to determine whether the disruptions in sleep that occur for many lactating females increase the risk of developing REDs.
Decreased libido: sexual dysfunction (ie, decreased libido, pain with intercourse) is common after childbirth, whether lactating or not.2 It is again important to differentiate the reasons for decreased libido in postpartum females.
Oligomenorrhea: lactating females have significant alterations in hormonal milieu compared with non-lactating females.7 High prolactin and low gonadotropin releasing hormone (GnRH) levels primarily drive normal physiological lactational amenorrhea (LAM). In addition, oestrogen, which suppresses milk production and adversely impacts milk quality, is substantially lower in lactating females than in non-menopausal, non-pregnant females.7 Lactating females also have decreases in pulsatile secretion of luteinising hormone (LH) and insulin, along with increased oxytocin and growth hormone (GH) levels.7 The duration of LAM is dependent on the frequency and duration of breast feeding/milk expression, with some studies finding up to 65% of lactating females experiencing LAM after 6 months postpartum.7 LEA leading to REDs in non-lactating athletes has also been associated with disruptions in several of these neuroendocrine metrics, including decreased GnRH, impaired LH release, decreased insulin, decreased oxytocin and resistance to GH.4 In a lactating female with REDs, decreases in oxytocin levels can be detrimental to lactation, as oxytocin stimulates the milk ejection reflex.7 In addition, oestrogen therapy has been used in non-lactating female athletes with REDs in clearly defined situations,4 but further research is needed to determine whether this is an option for athletes who wish to continue lactating.
Two or more career BSIs: both in the lactating female and the female athlete with REDs, low oestradiol levels increase the risk of BSIs due to increased bone resorption.4 7 In the lactating female, elevated prolactin also negatively impacts bone mineralisation and low parathyroid hormone-related protein may also adversely influence calcium metabolism.7 Both sedentary and active lactating females have been shown to be at an increased risk of BSIs,8 9 thus lactating athletes may experience BSIs even when bone mineral density is normal and calcium and vitamin D intake is sufficient.10
Urinary incontinence (UI): UI is frequently reported in the general postpartum population, particularly after vaginal and instrumented vaginal deliveries,2 as well as in nulligravid athletes with LEA.4 It is imperative that postpartum athletes with UI receive a full evaluation to determine factors contributing to UI.
Call for inclusion of lactating athletes in sport and exercise medicine research
Lack of female athlete representation in sport and exercise medicine (SEM) research has been well documented.11 A call has been made for inclusion of female athletes across the lifespan in SEM research, and guidelines for improving inclusion have been outlined.11 However, postpartum and lactating athletes remain overlooked. In addition, healthcare providers should be educated on safe return to sport guidelines for lactating female athletes. Further research on the intersection of REDs and lactating athletes, as well as the development of lactation-friendly assessment tools, are also needed.
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Footnotes
Twitter @ritadeeringPhD
Contributors Dr RED came up with the concept and was the primary author of the paper. Dr MLM revised the manuscript and provided guidance on updated REDs diagnostic criteria.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests MLM is an Associate Editor of the BJSM and a member of the editorial board of the BJSM IPHP.
Provenance and peer review Not commissioned; externally peer reviewed.