Table 2.

Summary of studies investigating infant hydration.

Study authors (citation)	Location	Study subjects	Study design	Hydration measures and cut-offs	Results	Authors' findings
Almroth and Bidinger (36)	India	Healthy infants aged 1–10 months (n = 44)	Quasi-experimental, using clinical measurements	USG and UO–cut-off values not reported	USG (of infants aged up to 6 months) = 1.004–1.036. UO = 66–1234 mml/l; mean = 1.011 (322 mml/l)	Under hot and dry conditions, healthy exclusively breast-fed infants do not require additional water.
Almroth (37)	Jamaica	Healthy EBF infants aged 2 weeks−4 months (n = 22)	Quasi-experimental, using clinical measurements	USG and UO–cut-off values not reported	USG = 1.005–1.015 (mean = 1.009). UO = 103–468 mml/l (mean = 258 mml/). Mean USG for individuals = 1.006–1.012 (UO = 139–358 mml/l).	Healthy, exclusively breast-fed infants can remain hydrated without supplementary water in a hot humid climate.
Armelini and Gonzalez (38)	Unknown “tropical” location	Healthy EBF infants aged 15–60 days (n = 8)	Cross-sectional, using clinical measurements	UO values below 200 mml/kg regarded as normal	Mean UO of samples collected at night = 137 mml/kg. Mean UO of samples collected in the afternoon = 171 mml/kg). Significant difference between means (p <0.01).	Urine osmalality was lower at night but did not exceed 200 mosmol/kg of water even in the hottest temperatures so supplementary water is likely not necessary for healthy exclusively breastfed infants in a hot and humid climate.
Ashraf et al. (39)	Pakistan	Healthy breastfed infants aged 2–4 months (n = 26)	Quasi-experimental, using clinical measurements	Water withheld for 8 days of study. Water given from day 8–15. DDAVP administered on day 15. USG values before and after the administration of DDAVP were compared. Haematocrit, sodium in breastmilk, and sodium in blood serum were compared at different stages to check for dehydration.	Significant increase in weight between day 1–8 and between day 8–15. No significant difference in haematocrit and serum sodium between day 8 and 1 and between day 15 and 8. No significant difference for USG between day 8 and 1. Significant increase in USG after infants received DDAVP.	Results indicate that the infants were not dehydrated when water was withheld and if needed, exclusively breastfed babies can concentrate urine when water is restricted
Brown et al. (40)	Peru	Breastfed infants aged <6 months (n = 40)	Quasi-experimental, using clinical measurements	Maximum USG 1.015 in the first few days of life, then 1.025–1.030 by 5 months	Standardized milk intakes = 4.0–12.1 gm/kg body weight per hour. Urine volume = 0.9–6.3 ml per kg body weight per hour. Max. USG in each infant 1.003–1.017. No associations between ambient temperature and urinary measures.	Healthy infants can maintain adequate hydration while exclusively breastfeeding in hot and humid conditions
Cohen et al. (41)	Honduras	EB LBW term male infants aged 0–4 months (n = 127)	Quasi-experimental, using clinical measurements	USG maximum below 1.018	Maximum USG = 1.001–1.012. USG associated with max. daily temperature only at 2 weeks of age. No association with humidity.	Results indicate that exclusively breastfed LBW infants do not require supplementary water, even under hot and humid conditions
Goldberg and Adams (42)	Unknown location in Sinai desert	Healthy EBF infants aged 40–150 days, from Bedouin villages (n = 15)	Cross-sectional, using clinical measurements	UO–cut-off values not reported	UO = 55–320 mmol/kg; mean = 164.5 mmol/kg	Supplementary water for breast-fed infants is not necessary to maintain hydration under hot and dry climatic conditions
Kusuma et al. (43)	India	Newborn infants with a gestational age of 350/7 weeks to 376/7 weeks born in a tertiary care hospital (n=205)	Cohort study, using a questionnaire and clinical measurements	Cumulative weight loss equal to or more than 10% was taken as ‘significant'. USG below 1.020 taken as normal.	No significant difference in weight loss or hypernatremia among the exclusively breastfed babies and partially breastfed babies	Near-term-born infants who are exclusively breastfed can maintain similar hydration status to that of PBF newborns in the first week after birth, even in summer months
Sachdev et al. (44)	Unknown “tropical” location	Healthy, male, exclusively breastfed babies aged 1–4 months attending a well-baby clinic (n = 45) AND doctors (n = 70) and nurses (n = 34) in the departments of pediatrics and obstetrics and gynecology in the same country	Quasi-experimental study using questionnaires, physical examinations, and clinical measurements	Breastmilk-intake, total fluid intake, urine output, UO, serum osmolality, weight change, rectal temperature. Cut-offs unclear. Compared study group (exclusively breastfed) with control group (partially breastfed)	Breastmilk intake and total fluid intake were significantly higher in the group that consumed only breastmilk compared to the control group after adjusting for confounders. No significant differences in urine output, urine or serum osmolality, weight change, or rectal temperature.	Exclusively breastfed babies don't require supplementary water in a tropical climate