Abstract
Background:
Breast milk is the optimal source of nutrition for newborns, especially preterm infants, and its temperature during feeding may influence both physiological stability and clinical outcomes. Although individual studies suggest potential benefits of warmed milk, evidence remains inconsistent and has not been comprehensively synthesized.
Objective:
To systematically review and analyze the effects of administering breast milk at different temperatures on physiological responses, feeding tolerance, and clinical outcomes in newborns.
Methods:
This systematic review and meta-analysis followed the Cochrane Handbook (version 6.0) and PRISMA guidelines. A comprehensive search of nine databases (CINAHL, CENTRAL, Web of Science, PubMed, Scopus, ScienceDirect, ERIC, EBSCO, OVID) was conducted for studies published between 2010 and 2025 in English. Data extraction and risk of bias assessment were performed independently by two reviewers using RoB-2 and ROBINS-I tools. Meta-analyses were conducted using Stata 16.0, applying fixed- or random-effects models based on I2 heterogeneity values.
Results:
Five studies involving 373 infants met the inclusion criteria. Meta-analyses revealed no statistically significant effects of breast milk temperature on heart rate, oxygen saturation, or body temperature at 5 or 30 minutes after feeding. A small short-term decrease in body temperature (5 minutes post-feeding) was noted in the intervention group, but this was not sustained. Time to achieve full enteral feeding was also not significantly different between groups. Heterogeneity was substantial for several outcomes (I2 > 85%). Risk of bias ranged from low to serious across included studies.
Conclusions:
Current evidence indicates that administering breast milk at different temperatures does not produce clinically meaningful differences in short-term physiological parameters or clinical outcomes in newborns. Milk at room temperature, near-body temperature, or alternative warming methods appears to be equally well tolerated.
Breast milk is the optimal source of nutrition for newborns and plays a critical role in supporting growth, immune function, and neurodevelopment. In particular, feeding preterm infants with breast milk has been shown to reduce complications such as necrotizing enterocolitis and sepsis, while also improving neurodevelopmental outcomes.1–4 When direct breastfeeding is not possible, breast milk is typically expressed, stored, and subsequently administered to the infant. This approach is especially essential for preterm or critically ill neonates in intensive care units who may be unable to breastfeed effectively. Stored expressed milk is also widely used by working mothers or in situations requiring close monitoring of milk production. However, factors such as storage duration, environmental temperature, container characteristics, and adherence to hygienic practices may influence the biological integrity of breast milk and, consequently, neonatal health. Understanding how these variables affect the nutritional and immunological quality of expressed breast milk is therefore of significant clinical importance.
The methods used for storing, thawing, and administering breast milk, including the temperature at which it is offered, may influence its nutritional composition as well as infants’ physiological responses. Recent studies have demonstrated that infants fed milk warmed to near-body temperature exhibit more stable postprandial heart rate and oxygen saturation levels.3,5,6 In contrast, a pilot study evaluating the physiological effects of feeding cold breast milk reported no significant changes in mesenteric blood flow or body temperature among preterm infants. Notably, cold milk was well tolerated and was associated with improved suck–swallow–breath coordination. 4 Collectively, these findings suggest that the temperature at which breast milk is administered may modulate infants’ physiological responses and feeding performance.
The temperature at which breast milk is administered during feeding represents an important variable influencing neonatal physiological stability and feeding comfort. Evidence from studies in preterm infants indicates differential tolerance between milk provided at room temperature and milk warmed to near-body temperature. In a randomized controlled trial (RCT), Uygur et al. reported that preterm infants fed milk at 32°C–34°C experienced significantly fewer episodes of apnea and reflux, demonstrated faster weight gain, and had shorter lengths of hospital stay. 7 Similarly, Çağlar et al. compared breast milk administered at varying temperatures and observed that infants receiving milk warmed to near-body temperature had significantly higher comfort scores. 3
In addition to physiological outcomes, the biochemical integrity of breast milk may be affected by the processes of thawing and warming. Siviroj et al. conducted a comparative analysis of different thawing and heating techniques and found that protein content was better preserved when rapid and controlled warming methods were used. These findings underscore the importance of feeding temperature not only for neonatal tolerance and physiological stability but also for maintaining the nutritional quality of expressed breast milk. 8
Moreover, the method used to warm expressed breast milk plays a substantial role in feeding outcomes. Evidence suggests that device-controlled warming techniques, as opposed to traditional warm water baths, contribute to improved weight gain and reduced length of hospital stay in preterm infants. Notably, preterm infants fed milk warmed with automated devices demonstrated significantly greater weight gain compared with those receiving milk heated using conventional methods. 5 These findings highlight the clinical relevance of employing standardized, controlled warming technologies to optimize neonatal growth and recovery.
Despite the clinical relevance of feeding temperature, the current evidence base remains remarkably limited. Existing studies are few in number, frequently involve small sample sizes, and demonstrate substantial methodological variability, limiting the generalizability of their findings. Furthermore, most available research focuses on isolated physiological parameters rather than providing a comprehensive evaluation of multiple neonatal outcomes. This scarcity of high-quality and systematically synthesized evidence highlights an important gap in the literature and underscores the need for rigorous investigation of how breast milk temperature influences neonatal health.
The existing body of literature indicates that the temperature at which breast milk is administered may influence both physiological responses and clinical outcomes in newborns. Despite these emerging findings, no systematic review or meta-analysis has comprehensively evaluated the effects of administering breast milk at different temperatures. Therefore, the present study aims to synthesize the available evidence and assess the impact of breast milk temperature on neonatal outcomes.
Method
Aim
This systematic review and meta-analysis was conducted to evaluate the effects of administering breast milk at different temperatures on feeding tolerance and clinical outcomes in newborns.
The research questions were:
How does the temperature at which breast milk is administered affect feeding tolerance in newborns, including preterm infants? What are the physiological responses (e.g., heart rate, oxygen saturation, body temperature, and suck–swallow–breath coordination) of newborns to breast milk given at different temperatures? Does the temperature of breast milk influence clinical outcomes such as weight gain, length of hospital stay, incidence of apnea, reflux, or other complications?
Design
This systematic review and meta-analysis was conducted to evaluate the effects of interventions using distraction cards on pain in children. The study was carried out in accordance with the Cochrane Handbook for Systematic Reviews of Interventions, version 6.0, and reported in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. 9
Search methods
A comprehensive literature search was conducted in the CINAHL, Cochrane Central, Web of Science, PubMed, Scopus, ScienceDirect, ERIC, EBSCO, and OVID databases, covering the period from 2010 to 2025. The search was limited to studies published in English. Search terms were developed using a combination of Medical Subject Headings and keywords extracted from relevant articles. Initially, titles and abstracts of all retrieved records were screened to assess eligibility based on predefined inclusion criteria. Full texts were reviewed when available. For studies where the full text could not be accessed, authors were contacted directly; nevertheless, studies without accessible full text were excluded, even if their abstracts met inclusion criteria. Studies were included according to the PICOS framework (Population, Intervention, Comparison, Outcomes, Study Design) to ensure a structured and rigorous selection process (Fig. 1). 10
Flow diagram of study retention process for the meta-analysis and systematic review.
Inclusion and Exclusion Criteria
Inclusion criteria
Studies with a randomized controlled, quasi-experimental, or comparative cohort design. Participants: Preterm (<37 weeks) or term neonates. Intervention: Administration of breast milk at different temperatures. Comparator: Alternative temperature groups or standard clinical practice. Outcome measures:
Primary outcomes: Physiological parameters (body temperature, spo2, heart rate) and discharge time.
Exclusion criteria
Animal studies, case reports, and purely in vitro experiments. Studies focusing solely on pasteurization methods or milk composition without reporting clinical feeding outcomes. Studies for which the full text was not accessible.
Search outcome
The initial search yielded a total of five studies potentially eligible for inclusion in this systematic review and meta-analysis. Duplicate records were removed in the first step. Subsequently, studies that were irrelevant based on titles and/or abstracts were excluded. Ultimately, five full-text studies meeting the predefined inclusion criteria were included in the systematic review and meta-analysis (Fig. 1).
Risk of bias and quality appraisal
To minimize bias, literature screening, study selection, data extraction, and quality assessment were independently conducted by two researchers in three stages. First, duplicates were removed, and titles and abstracts were screened for eligibility; data were checked for accuracy and consistency, with disagreements resolved through discussion. Second, full texts were evaluated against inclusion and exclusion criteria to finalize studies for inclusion. Finally, the risk of bias of included RCTs was assessed independently by two researchers using the Cochrane Collaboration’s tool for assessing risk of bias in randomized trials, which evaluates 12 domains as low, unclear, or high. Discrepancies were discussed and resolved until consensus was reached. 11
Data extraction and synthesis
Data extraction was independently performed by two researchers using a standardized form, capturing study characteristics such as first author, publication year, country, sample size (intervention/control), intervention procedures, measurements, and outcomes. For the meta-analysis, data were analyzed using Stata 16.0. All available post-intervention measurements were included, and pain scores served as the primary outcome. Data extraction was cross-checked using Microsoft Excel. Effect sizes were calculated using Cohen’s d (0.2 = small, 0.5 = medium, 0.8 = large). Heterogeneity among studies was assessed using I2 statistics, with I2 > 50% indicating substantial heterogeneity and prompting the use of a random-effects model, whereas I2 ≤ 50% led to a fixed-effects model. Random-effects analyses were performed using the DerSimonian-Laird method.11,12
Results
The characteristics of the included studies and details regarding the interventions are presented in Table 1. The five studies included in this review were conducted between 2019 and 2025 and involved neonatal samples ranging from 48 to 150 participants.3–5,7,13 In total, the studies comprised 373 infants. Four of the studies were conducted in Turkey, while one study was carried out in Spain.
Characteristics of the Studies Included in the Meta-Analysis
Across the studies, two investigations reported outcomes related to physiological vital signs,3,4 three assessed body temperature,3,4,13 and two examined the time to achieve full enteral feeding.5,7 In most studies, the control groups received no specific intervention beyond standard care, whereas the intervention groups were exposed to warmed breast milk at various temperatures, most commonly 32°C–34°C or 37°C.
Risk of bias in the included studies
Four studies3,5,7,13 were evaluated using the RoB-2 tool, while the nonrandomized pretest–posttest controlled study by Aktaş et al. (2023) 4 was assessed with the ROBINS-I instrument. Examination of the overall risk of bias across the five included studies indicated that the randomized/crossover trials generally demonstrated low to moderate risk of bias, with only one study 13 exhibiting a high risk of bias in the outcome measurement domain. The single nonrandomized study was classified as having a serious risk of bias according to ROBINS-I. Overall, the included evidence base can be considered methodologically acceptable; however, the interpretation of the findings should take into account the potential biases introduced by the nonrandomized design of one study (Tables 2 and 3).
Risk of Bias Assessment for Randomized and Crossover Studies (RoB-2)
Risk of Bias Assessment for the Nonrandomized Study (ROBINS-I)
Results
Study outcomes of the experimental group at room temperature
Across the included studies, meta-analytic comparisons of physiological outcomes indicated no statistically significant differences between the intervention group (receiving warmed milk) and the control group. Detailed findings for each parameter are presented below.
Heart rate
The meta-analysis examining heart rate measured 5 minutes post-feeding demonstrated substantial heterogeneity among studies (I2 = 85.75%). Using a random-effects model, no significant effect of milk-warming temperature on heart rate was identified (d = 0.06, p = 0.89) (Fig. 2).
Forest plot of the meta-analysis for heart rate measured 5 minutes after feeding in intervention and control groups.
Similarly, the analysis of heart rate measured 30 minutes after feeding revealed high heterogeneity (I2 = 84.69%). The random-effects model indicated no statistically significant difference between intervention and control groups (d = –0.26, 95% CI: –1.15 to 0.63, p = 0.57) (Fig. 3).
Forest plot of the meta-analysis for heart rate measured 30 minutes after feeding in intervention and control groups.
Body temperature
For body temperature measured 5 minutes post-feeding, no heterogeneity was observed across studies (I2 = 0.0%). The fixed-effect inverse-variance model showed no significant difference between groups (d = –0.24, 95% CI: –0.56 to 0.09, p = 0.15) (Fig. 4).
Forest plot of the meta-analysis for body temperature measured 5 minutes after feeding.
Body temperature measured 30 minutes after feeding demonstrated low heterogeneity (I2 = 22.19%). Consistent with earlier findings, the fixed-effect model revealed no statistically significant difference between intervention and control groups (d = –0.18, 95% CI: –0.46 to 0.11, p = 0.22) (Fig. 5).
Forest plot of the meta-analysis for body temperature measured 30 minutes after feeding.
Oxygen saturation (SpO2)
For SpO2 assessed 5 minutes after feeding, no heterogeneity was detected (I2 = 0.0%). The fixed-effect model showed no significant differences between groups (d = 0.17, 95% CI: –0.15 to 0.50, p = 0.29) (Fig. 6).
Forest plot of the meta-analysis for oxygen saturation (SpO2) measured 5 minutes after feeding.
In contrast, SpO2 measured 30 minutes post-feeding exhibited moderate heterogeneity (I2 = 49.21%). Although the fixed-effect model suggested a trend toward higher oxygen saturation levels in the intervention group, this effect did not reach statistical significance (d = 0.31, 95% CI: –0.02 to 0.63, p = 0.06) (Fig. 7).
Forest plot of the meta-analysis for oxygen saturation (SpO2) measured 30 minutes after feeding.
Study outcomes of the experimental groups receiving milk at temperatures different from room temperature
Heart rate
The meta-analyses evaluating heart rate at 5 and 30 minutes after feeding demonstrated that alternative breast milk-warming interventions did not produce significant physiological changes compared with control conditions. At 5 minutes post-feeding, the pooled effect showed no statistically significant difference between groups (Cohen’s d = –0.25, 95% CI: –1.37 to 0.86, p = 0.66) despite very high heterogeneity (I2 = 90.20%). Similarly, at 30 minutes post-feeding, the intervention continued to show no significant effect on heart rate (Cohen’s d = –0.29, 95% CI: –1.21 to 0.64, p = 0.54), with heterogeneity remaining substantial (I2 = 85.80%). Overall, these findings indicate that variations in milk-warming methods do not appear to influence the short-term heart rate responses of preterm infants (Figs. 8 and 9).
Forest plot of the meta-analysis for heart rate measured 5 minutes after feeding in intervention and control groups.
Forest plot of the meta-analysis for heart rate measured 30 minutes after feeding in intervention and control groups.
Body temperature
The meta-analyses evaluating body temperature at 5 and 30 minutes after feeding revealed differing short-term and mid-term effects of the intervention. At 5 minutes post-feeding, no heterogeneity was detected between studies (I2 = 0.00%), and the fixed-effects model showed a small but statistically significant decrease in body temperature in the intervention group (d = –0.49, 95% CI: –0.82 to –0.16, p = 0.00). However, by 30 minutes post-feeding, moderate heterogeneity emerged (I2 = 54.41%), and the random-effects model demonstrated no statistically significant difference between the intervention and control groups (d = –0.30, 95% CI: –0.81 to 0.20, p = 0.24). Overall, these findings suggest that while the intervention may cause a slight and immediate reduction in body temperature shortly after feeding, this effect does not persist at 30 minutes (Figs. 10 and 11).
Forest plot of the meta-analysis for body temperature measured 5 minutes after feeding.
Forest plot of the meta-analysis for body temperature measured 5 minutes after feeding.
Oxygen saturation
Across both time points—5 minutes and 30 minutes after feeding—the meta-analyses demonstrated very high heterogeneity (I2 = 90.99% and I2 = 89.06%, respectively), indicating substantial variability in study findings. Using random-effects DerSimonian–Laird models, neither analysis showed a statistically significant effect of the intervention on oxygen saturation. At 5 minutes, the pooled effect size was d = 0.54 (95% CI: –0.63 to 1.72, p = 0.36), and at 30 minutes, the pooled effect was d = 0.47 (95% CI: –0.59 to 1.53, p = 0.39). Overall, these findings suggest that the intervention did not produce a meaningful change in SpO2 levels at either post-feeding time point (Figs. 12 and 13).
Forest plot of the meta-analysis for oxygen saturation (SpO2) measured 5 minutes after feeding.
Forest plot of the meta-analysis for oxygen saturation (SpO2) measured 30 minutes after feeding.
Time to achieve full enteral feeding
This figure presents the meta-analysis comparing the time required to achieve full enteral feeding between the intervention and control groups, using standardized mean differences (Cohen’s d). A very high level of heterogeneity was observed across studies (I2 = 89.06%), indicating substantial variability in effect sizes. Based on the random-effects DerSimonian–Laird model, the pooled effect showed no statistically significant difference between groups (d = 0.47, 95% CI: –0.59 to 1.53, p = 0.39). These findings suggest that the intervention did not significantly shorten or delay the transition to full enteral feeding (Fig. 14).
Forest plot of the meta-analysis for time to Achieve Full Enteral Feeding Between Intervention and Control Groups.
Discussion
This systematic review and meta-analysis is among the first to comprehensively evaluate the effects of administering expressed breast milk at different temperatures on neonatal physiological stability and clinical outcomes. Across five eligible studies, the overall findings indicate that variations in milk temperature, whether room temperature, near-body temperature, or alternative warming methods, do not produce clinically significant changes in short-term physiological parameters or broader clinical outcomes in newborns.
Physiological responses such as heart rate, oxygen saturation, and body temperature showed no significant differences between infants fed warmed milk and those receiving milk at room temperature or standard clinical conditions. Despite substantial heterogeneity across the included studies, particularly for heart rate and oxygen saturation (I2 > 85%), the pooled effect sizes consistently demonstrated the absence of meaningful physiological impact. These findings contrast with some individual studies suggesting improved postprandial stability with warmed milk.3,5 However, the variability in sample characteristics, intervention temperatures, warming techniques, and measurement time points across studies likely contributed to the observed inconsistencies.
In relation to body temperature, a small but statistically significant reduction immediately after feeding (5 minutes) was detected in infants receiving warmed milk, although this effect did not persist at 30 minutes. This transient change is unlikely to be clinically relevant and may reflect short-term thermal adjustments rather than sustained thermoregulatory differences. Importantly, these results align with the findings of Aktaş et al., 4 who reported that cold milk is well tolerated by preterm infants without adverse thermoregulatory consequences.
Oxygen saturation (SpO2) similarly showed no significant differences at either 5 or 30 minutes post-feeding, although a nonsignificant trend toward higher SpO2 at 30 minutes in the intervention group was observed. This trend is consistent with hypotheses that warmed milk may enhance feeding comfort or reduce energy expenditure; however, it does not reach statistical or clinical significance based on current evidence.
Regarding clinical outcomes, particularly the time required to achieve full enteral feeding, the meta-analysis revealed no significant differences between groups. This finding contrasts with some original studies reporting improved gastrointestinal tolerance and shorter hospitalization among infants receiving warmed milk.5,7 Nevertheless, the high heterogeneity observed and the limited number of studies available suggest caution in interpreting these isolated results.
A notable strength of this review is the systematic and methodologically rigorous evaluation of multiple physiological and clinical outcomes. However, this synthesis also highlights important gaps in the literature. The included studies exhibit considerable methodological diversity, including different intervention temperatures, inconsistent warming devices, heterogeneous measurement timing, and varied definitions of feeding tolerance. Moreover, one nonrandomized study presented a serious risk of bias, and sample sizes in several studies were modest, limiting the precision and generalizability of pooled estimates.
Despite these limitations, the collective evidence suggests that feeding expressed breast milk at temperatures other than room temperature, whether cooler or warmer, does not confer significant physiological or clinical benefits in the short term. Importantly, the findings support the safety of administering milk at a range of temperatures commonly encountered in clinical practice. Nonetheless, given the substantial heterogeneity across studies, further large-scale, well-designed RCTs are warranted. Future research should prioritize standardized temperature protocols, consistent measurement time points, and assessment of additional clinically relevant outcomes, including energy expenditure, behavioral cues, feeding efficiency, gastrointestinal tolerance, and long-term neurodevelopment.
Authors’ Contributions
Ç.G. and T.T.: Conceptualization, methodology, investigation, formal analysis, data curation, writing—original draft, writing—review and editing, visualization, supervision, project administration. Both authors contributed equally to all aspects of the work.
Footnotes
Author Disclosure Statement
No competing financial interests exist.
Funding Information
This research received no external funding.