Researchers in Tanzania discovered that the month a baby is born can affect their body chemistry and development for at least the first year and a half of life. By studying babies born during different seasons, scientists found that babies born during times of food shortage had different chemicals in their blood and urine compared to babies born when food was plentiful. These chemical differences were connected to how well babies grew, how smart they were becoming, and even how well certain nutritional treatments worked. The findings suggest that babies born during lean seasons need special attention and different types of nutrition help to catch up with babies born during better times.

The Quick Take

  • What they studied: Whether the season a baby is born in affects the chemicals in their body and how well they develop during their first 18 months of life
  • Who participated: Tanzanian infants and their mothers from rural communities where food availability changes dramatically with the seasons. The study followed babies from birth through 18 months old, measuring chemicals in their blood and urine, and testing their thinking and learning skills
  • Key finding: Babies born during seasons with less food available had different body chemistry patterns compared to babies born when food was plentiful. These differences lasted at least 18 months and were connected to how well babies grew and how their brains developed
  • What it means for you: If you live in an area with seasonal food shortages, knowing your baby’s birth season might help doctors and nutritionists give better, more targeted help. This research suggests one-size-fits-all nutrition programs may not work as well as programs designed for specific seasons. However, this study was done in Tanzania, so results may differ in other places

The Research Details

This was a secondary analysis, meaning researchers looked at information already collected from a larger study called ELICIT that followed mothers and babies in rural Tanzania. The original study was designed to test whether giving mothers a specific vitamin (nicotinamide) would help babies grow better. For this new analysis, scientists measured hundreds of different chemicals in babies’ blood and urine at different ages and compared them based on which month the babies were born. They also measured how much food was available during different seasons, tested breast milk composition, and checked babies’ thinking and learning skills at 18 months old.

The researchers used advanced laboratory techniques to identify and measure metabolites—the tiny chemical building blocks that our bodies create when we eat food and use energy. They then looked for patterns in these chemicals that matched up with birth season, food availability, and how well babies were developing.

This approach allowed scientists to see the bigger picture of how seasonal food shortages affect not just what babies eat, but the actual chemistry happening inside their bodies during critical growth periods.

Understanding how birth season affects baby development is important because it could help doctors and health workers provide better, more targeted help to babies born during difficult seasons. Rather than giving all babies the same nutrition support, this research suggests we might need different approaches depending on when babies are born. This is especially important in places where food availability changes dramatically throughout the year

This study was published in Nature Communications, a highly respected scientific journal. The research used advanced laboratory methods to measure hundreds of different body chemicals, which is more detailed than simpler studies. However, because this was a secondary analysis (looking at data collected for a different purpose), the researchers couldn’t control all the factors they might have wanted to. The study was done in one region of Tanzania, so results might be different in other parts of the world with different seasonal patterns or food systems

What the Results Show

The main discovery was that babies’ body chemistry followed clear seasonal patterns based on their birth month. Babies born during seasons with less food available had different levels of important chemicals in their blood and urine compared to babies born during seasons with plenty of food. These differences weren’t just temporary—they lasted at least 18 months, showing that birth season creates long-lasting changes in how babies’ bodies work.

The study found that several important chemicals were affected by birth season, including choline (which helps brain development), trimethylamine-N-oxide (which comes from food), and polyunsaturated fatty acids (healthy fats important for growth). These aren’t random chemicals—they’re specifically important for how babies’ brains and bodies develop.

Babies’ thinking and learning skills at 18 months also followed seasonal patterns matching their birth month. Babies born during food-scarce seasons showed different developmental patterns compared to babies born during abundant seasons. The seasonal chemicals in their bodies were connected to these developmental differences, suggesting the body chemistry changes might actually be causing the developmental differences.

Interestingly, a vitamin treatment (nicotinamide) that was supposed to help all babies grow better worked differently depending on babies’ birth season and their body chemistry patterns. This suggests that one-size-fits-all treatments might not be as effective as treatments designed for specific seasons

The research showed that breast milk composition also changed with the seasons, which helps explain why babies’ body chemistry changed. Mothers produced different types of milk during different seasons, likely because their own diets changed with food availability. This mother-to-baby connection through breast milk appears to be one way seasonal food shortages affect babies’ development. The study also confirmed that rainfall patterns and food insecurity were directly connected to the chemical changes seen in babies’ bodies

Previous research has shown that birth season can affect health and development, but most studies only looked at simple measures like birth weight or disease rates. This study goes much deeper by measuring the actual chemicals in babies’ bodies, providing a more detailed explanation of how season affects development. The findings support earlier research showing that the period around birth is especially important for long-term health, and add new evidence that this happens through changes in body chemistry. The connection between season, food availability, and brain development is relatively new and important for understanding why some babies in resource-limited areas develop differently

This study was done only in rural Tanzania, so results might not apply to other countries or cities with different food systems and seasons. The researchers couldn’t randomly assign babies to be born in different seasons (obviously!), so they couldn’t prove that season directly causes the chemical changes—only that they’re connected. The study measured chemicals at specific time points, so researchers might have missed important changes that happened between measurements. Additionally, many factors affect baby development besides season and food availability, and this study couldn’t control for all of them. The original study was designed to test a vitamin treatment, not to study seasonal effects, so some important information might not have been collected

The Bottom Line

For families in areas with seasonal food shortages: Work with local health workers to plan nutrition support that matches your baby’s birth season rather than using the same approach year-round (moderate confidence). Consider tracking your baby’s growth and development more carefully if born during lean seasons (moderate confidence). For health programs: Design nutrition interventions that account for birth season and seasonal food patterns rather than one-size-fits-all approaches (moderate confidence). For researchers: More studies are needed in different regions to see if these findings apply elsewhere (low to moderate confidence)

This research is most relevant for families and health workers in rural areas of Africa and other regions where food availability changes dramatically with seasons. It’s particularly important for pregnant women and mothers of young babies in these areas. Health programs and governments working on child nutrition and development in resource-limited settings should pay attention to these findings. People in developed countries with stable food supplies year-round may see less direct benefit, though the research adds to our general understanding of how nutrition affects baby development

The chemical changes in babies’ bodies appear to happen during pregnancy and early infancy and persist for at least 18 months. The effects on thinking and learning skills were measurable by 18 months. However, it’s unclear if these effects last into childhood and adulthood—that would require longer follow-up studies. Improvements from better seasonal nutrition support would likely take weeks to months to show up in body chemistry, and longer to see effects on growth and development

Want to Apply This Research?

  • Track your baby’s birth month and current season, then log monthly measurements of: weight gain (in pounds or kilograms), head circumference growth, and developmental milestones (first smile, rolling over, sitting up, etc.). Compare your baby’s progress to growth charts that account for birth season rather than assuming all babies should follow the same pattern
  • If your baby was born during a lean season: (1) Work with a health worker to create a season-specific nutrition plan for your baby and yourself if breastfeeding, (2) Track which foods are available in each season and plan ahead for lean months, (3) Consider timing future pregnancies if possible to avoid conception during seasons that would result in birth during food-scarce months, (4) Keep detailed records of your baby’s growth to share with health workers
  • Set monthly reminders to measure and record your baby’s weight, length, and head circumference. Create a simple chart showing your baby’s growth across seasons to identify any patterns. Share this information with your health worker at regular check-ups. If your baby was born during a lean season, pay extra attention to developmental milestones and discuss any concerns with your health worker early

This research describes associations between birth season and infant development in a specific population in Tanzania and should not be interpreted as medical advice. Individual babies develop at different rates regardless of birth season. If you have concerns about your baby’s growth or development, consult with your pediatrician or health care provider. This study suggests that seasonal factors may influence development, but does not prove that birth season directly causes developmental differences. Nutrition and healthcare decisions should be made in consultation with qualified health professionals who know your specific situation. The findings from this Tanzanian study may not apply to all populations or regions with different food systems and climates.