Even when infants are born free of HIV, they often face significant health challenges. A new study published in Nature Communications on October 28, 2025, provides fresh insight into why these children struggle with developmental delays and other medical problems. Researchers have identified a missing nutrient in the breast milk of women living with HIV that could play a crucial role in their babies’ health outcomes.
The study points to a deficiency of tryptophan, an essential amino acid vital for immune function, growth, and brain development. According to the findings, breast milk from women with HIV contains markedly lower levels of tryptophan, even when the mothers are receiving effective antiretroviral therapy (ART).
Key Findings: A Persistent Metabolic Signature
Lead author Dr. Nicole Tobin, professor of pediatrics at UCLA’s David Geffen School of Medicine, emphasized the significance of the discovery.
“What’s particularly striking is that this metabolic signature persists even when mothers are on effective antiretroviral therapy,” Dr. Tobin explained in a news release. “That helps explain why these children continue to need extra support despite advances in HIV treatment.”
The research team analyzed more than 1,400 breast milk samples collected from 326 women in Zambia, of whom 288 were living with HIV. Their analysis revealed that tryptophan levels in the breast milk of HIV-positive mothers were about 50% lower than those of HIV-negative mothers.
Interestingly, the mothers themselves also showed lower blood tryptophan concentrations. This suggests that their bodies may prioritize retaining the amino acid for their own physiological needs, leaving less available to transfer through breast milk to their infants.
A Global Health Concern: Millions of Children at Risk
Each year, an estimated 1.3 million children are born to women living with HIV worldwide. Antiretroviral therapy has dramatically reduced the risk of mother-to-child transmission of the virus. However, even in cases where infection is prevented, children born to these mothers remain vulnerable.
In low-income countries, such children are still 50% more likely to die in early childhood compared with those born to HIV-negative women. They also experience higher rates of infections, stunted growth, and delayed cognitive development, underscoring the complexity of the health disparities associated with maternal HIV.
The new research suggests that these poor outcomes might not solely stem from social or environmental factors, but also from biochemical differences in maternal metabolism and nutrition.
Understanding Tryptophan’s Role in Infant Health
Tryptophan is a critical building block for several biological functions. It contributes to the synthesis of serotonin (important for mood and brain development), melatonin (which regulates sleep), and niacin (essential for energy production and cellular repair). A deficiency during infancy could therefore disrupt several systems at once—immune defense, growth, and neurological development.
The findings indicate that HIV infection alters maternal metabolism, reducing the availability of tryptophan even when viral replication is suppressed by ART. This metabolic shift may explain why infants of HIV-positive mothers show developmental and immune differences that have puzzled scientists for years.
Future Directions: Supplementation and Interventions
The UCLA research team believes their findings could open new avenues for interventions. They recommend further studies to determine whether tryptophan supplementation—either for mothers or infants—could mitigate these health challenges.
“We’ve known for years that children born to mothers living with HIV face greater health challenges, but we didn’t fully understand why,” said Dr. Grace Aldrovandi, chief of infectious diseases at UCLA’s David Geffen School of Medicine and senior author of the study. “This study reveals that tryptophan deficiency and altered metabolism may serve as a common denominator explaining the immune, growth, and cognitive differences we see in these children.”
The research team is now planning to test this hypothesis using animal models to evaluate how nutritional supplementation could improve outcomes.
Implications for Global Maternal and Child Health
This study underscores the importance of integrating nutritional assessment into HIV care for pregnant and breastfeeding women. While ART remains essential to prevent viral transmission, addressing metabolic and nutritional deficiencies could represent the next frontier in improving the long-term health of children born to HIV-positive mothers.
As global health organizations continue to combat pediatric HIV, findings like these offer a crucial reminder: viral suppression alone is not enough. Supporting maternal nutrition—particularly amino acid balance—could be key to giving every child, regardless of maternal HIV status, a healthy start in life.
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