Objective: To investigate the effects of calcium and probiotics on the incidence and duration of acute diarrhea and acute respiratory tract infections (ARTIs) in low-socioeconomic communities of Jakarta, Indonesia.

Methods: We conducted a 6-month, double-blind, placebo-controlled study in 494 healthy children aged 1 to 6 years who received low-lactose milk with low calcium content (LC; ∼50 mg/day; n = 124), regular calcium content (RC; ∼440 mg/day; n = 126), RC with 5×10⁸ colony-forming units per day of Lactobacillus casei CRL431 (n = 120), or RC with 5×10⁸ colony-forming units per day of Lactobacillus reuteri DSM17938 (n = 124). Number and duration of diarrhea and ARTIs episodes were primary and secondary outcomes, respectively.

Results: Incidence of World Health Organization-defined diarrhea (≥3 loose/liquid stools in 24 hours) was not significantly different between RC and LC (relative risk [RR]: 0.99 [95% confidence interval (CI): 0.62-1.58]), between L. casei and RC (RR: 1.21 [95% CI: 0.76-1.92]), or between L. reuteri and RC (RR: 0.76 [95% CI: 0.46-1.25]) groups. Incidence of all reported diarrhea (≥2 loose/liquid stools in 24 hours) was significantly lower in the reuteri versus RC group (RR: 0.68 [95% CI: 0.46-0.99]). Irrespective of the definition used, L. reuteri significantly reduced diarrhea incidence in children with lower nutritional status (below-median height-and-weight-for-age z score). None of the interventions affected ARTIs.

Conclusions: RC milk, alone or with L. casei, did not reduce diarrhea or ARTIs in Indonesian children. L. reuteri may prevent diarrhea, especially in children with lower nutritional status.