Many young and physically active people have low iron stores, and iron supplements are often used to prevent iron deficiency. A new PhD thesis from NMBU shows that low-dose iron supplementation may help maintain iron levels without harming the gut microbiota. At the same time, the research suggests that a high intake of sulfur-containing amino acids may influence gut bacteria in potentially unfavourable ways.
The doctoral research of Stine Sofie Strømland explores how iron and sulfur-containing amino acids affect the gut microbiota and human health. Findings from studies involving athletes, military recruits, and individuals with overweight and obesity provide new insights into the relationship between diet, gut bacteria, and health.
Below, she answers four questions about her research:
Why is this research important?
This PhD project investigated how two dietary components, iron and sulfur-containing amino acids, affect health, with a particular focus on the gut microbiota.
This is important because iron deficiency is common among athletes, especially women, and can reduce physical performance. Iron supplements are often used to prevent or treat iron deficiency, but high doses may cause gastrointestinal discomfort. One possible explanation is that excess iron that is not absorbed in the intestine affects the bacteria living there. However, this has received limited attention in research, particularly among athletes.
Diet also plays an important role. Red meat is an important source of iron, but it also contains sulfur-containing amino acids which is part of the protein. High intakes of these amino acids have been linked to adverse health effects. Animal studies have shown that they may affect the gut microbiota, but this has so far been investigated only to a limited extent in humans.
What was the aim of your PhD project?
The aim of the research was to assess iron status in healthy, physically active individuals, investigate how high physical strain affects iron levels, and test whether a low-dose iron supplement could prevent iron levels from declining without causing unwanted side effects.
A particular focus was to examine whether iron supplementation influences the gut microbiota.
The project also investigated how a high intake of the sulfur-containing amino acids methionine and cysteine, which the body uses to build proteins, affects the gut microbiota and levels of inflammation in the body.
The PhD project included three studies: one involving male and female military recruits participating in the selection process for the Norwegian Armed Forces Special Operations Forces, one involving female football players, and one involving men and women with overweight or obesity.
What are your most important findings?
The results showed that a large proportion of both male and female military recruits, as well as the female football players, had low iron levels. Demanding military field exercises further weakened iron status among the recruits.
Among the football players, low-dose iron supplementation helped maintain iron levels throughout the season without causing negative changes in the gut microbiota or in other health measures that were assessed. On the contrary, the researchers observed greater bacterial diversity in the gut among the players who received supplementation. High bacterial diversity is often regarded as a sign of a healthy gut microbiota. Taken together, the results suggest a positive effect of the low-dose supplement.
The study of sulfur-containing amino acidsfound that participants with high intakes had lower bacterial diversity and a greater abundance of certain bacteria that have previously been linked to adverse health effects. They also showed signs of increased inflammation in the gut.
Overall, the results indicate a possible negative effect of a high intake of these amino acids, which are found in greater amounts in foods of animal origin than in plant-based foods.
What impact could your research have within the field and in a broader context?
This PhD project contributes new knowledge about how iron and sulfur-containing amino acids influence the gut microbiota and human health.
The findings suggest that many young and physically active individuals do not have optimal iron stores, and that low-dose iron supplementation may be a gentle strategy for preventing iron levels from falling during periods of intensive training.
Since the study shows signs that a high intake of sulfur-containing amino acids disrupts the balance of gut bacteria, the findings may help explain why a high consumption of red meat has been associated with poorer health outcomes in previous research. However, more research is needed to confirm this hypothesis.
Taken together, the findings may provide an important basis for further research and contribute to more targeted dietary and nutritional recommendations in the future.
FAct box:
Stine Sofie Strømland
- Previous education: Bachelor's and Master's degrees in Biotechnology from NMBU
- From: Ski, Norway
- Degree completed: PhD at the Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU)
- Main supervisor: Professor Siv Kjølsrud Bøhn
- Thesis title in Norwegian and English:
- Jern og svovelholdige aminosyrer: påvirkning på tarmmikrobiota og helse
- Iron and sulfur amino acids: impacts on gut microbiota and health