Effect of Altitude on Iron Absorption in Iron Depleted Women

Populations living at higher altitudes may have higher iron requirements, as body iron is naturally increased in long-term high-altitude residents to compensate for the lower oxygen partial pressure. A residence altitude of 3600 masl implies an increase in Hemoglobin of ≈30 g Hb/l, which would correspond, in a 60 Kg woman to an increase of ≈500 mg red blood cell iron. Early studies in Bolivia have suggested decreased iron stores in women living at altitudes >3000 masl, compared to their counterparty living below 3000 masl .

The short-term exposure to high altitudes has profound impacts on iron metabolism. The lower oxygen partial pressure increases the rate of red blood cell synthesis, which is reflected in decrease in iron status parameters such as serum iron, serum ferritin, and an increase in erythropoietin and erythroferrone which in turn downregulate hepcidin, the master regulator of systemic iron metabolism , affecting iron release from stores and dietary iron absorption . In addition, intracellular oxygen sensors, the prolyl hydrolases (PHD's), stabilize hypoxia inducible factors (HIF-1α and HIF2-α) critically controlling transcriptional regulators such as dimetal transporter-1 (DMT-1) responsible for apical iron absorption in enterocytes .

Early studies in Peru by Huff et al. showed marked short-term increases of serum iron incorporation in red blood cells in subjects native from Lima (sea level) during acclimatization at Morococha, at 4540 masl. The opposite was the case in Morococha natives during acclimatization in Lima, as they had a decreased rate of plasma iron transfer to red blood cells . Notably however, during the short duration of the study (10 days) no marked change in red cell volume, hemoglobin or red cell mass could be detected.

Despite these well-described biologic mechanisms and short-term effects on physiological markers of iron status, the effects of chronic exposure to high altitude on iron status, body iron compartments and dietary iron requirements are incompletely understood. Genetic factors as reflected by different ethnicities are considered to play a large role in altitude-induced adaptations in iron metabolism .

A recent large study (n=71798) conducted in young male and iron replete Swiss army conscripts suggests a steady increase in hemoglobin and ferritin with increasing altitude, an increase that was detectable with each 300 masl increase, starting with as low as 300 masl of altitude. The authors also suggested that in this population, serum ferritin rose with altitude, independently from the increase in hemoglobin , suggesting a separate biological mechanism driving iron stores with increasing altitude. This data contrasts with data from Bolivia in apparently healthy women of reproductive age, where body iron stores were decreased at altitudes >3000 masl , compared to women living at lower altitudes (<3000 masl), suggesting that at high altitude, iron availability may be a limiting factor for optimal iron stores and for anemia prevention. More research is therefore needed on the determinants of iron balance in function of altitude, namely the interplay between dietary iron absorption, iron status, and iron status markers.

The primary objective of the proposed research is to determine iron bioavailability of iron from biofortified potatoes at different altitudes in populations of Andean descent. Human trials will be undertaken with volunteers in the Huancavelica region of Peru (elevation: 3676 meters) as well as in Lima (elevation close to sea level). The aim is to assess the effect of altitude on the absorption from a promising iron biofortified potato cultivar. These trials require incorporation of iron stable isotopes into the meals of the bio fortified and the analysis of the isotopes in subsequent blood (red blood cells) samples.