Optimizing Iron Levels

Low iron in runners: how fuelling (or under-fuelling) might be contributing to your chronically low levels

Written by Dr. Fiona Callender, ND

Endurance athletes often struggle with getting iron levels high enough - whether they suffer with anemia or not. This can impact performance but also how they feel day-to-day. Ask anyone who has had chronically low levels and then gets a transfusion - it makes a huge difference! The challenge with getting enough (and keeping enough) iron is related to a few key factors including: higher needs in athletes, higher rates of breakdown, and reduced absorption. Often, the instruction is to take an iron supplement and add more high-iron foods - both great recommendations - but we may be missing a key dietary factor that impacts how we absorb iron: carbohydrates.

To understand why adding more carbohydrates might be a key nutritional factor you are missing, we have to bring it back to the basics of iron, how it is used, and how it is absorbed. We explore why endurance athletes have such a challenge maintaining their levels.

UNDERSTANDING IRON METABOLISM

When you get blood work, you will notice hemoglobin and ferritin as two important factors in assessing iron deficiency. Hemoglobin is in our red blood cells and helps carry oxygen to our muscles. We require iron to make hemoglobin. When we don’t have enough iron to make more hemoglobin we call this iron deficiency anemia. This happens as a very late stage of iron deficiency because making red blood cells is such a priority for the body. Once we have anemia, iron deficiency has probably been present for a while.

We can also have iron deficiency without anemia. We can see this with a low ferritin level on blood work but adequate hemoglobin levels. Iron deficiency (even without anemia) can impact aerobic capacity because we require iron for chemical reactions involved in making energy (ATP) as well as building hemoglobin.

Highly Active People Lose More Iron

Iron is tightly regulated in our body because too much isn’t great for us either. We are in a constant balance between absorption and loss - only absorbing about 10% of the iron we take in through food, and losing about 1mg per day as waste. We lose iron through sweat and skin, through our gut, our urine and for many, menstruation. At baseline, without menstruation, we are barely breaking even if we meet basic iron intake through food (the recommended daily intake (RDA) is 8-10g). Runners also have a breakdown of red blood cells through the actual pounding of pavement! When the foot strikes the ground, there is physical damage to red blood cells in the legs. Exercise related damage may also happen through the high rate of red blood cells passing through tiny capillaries in the muscle - trying to get more oxygen to the working muscles. None of this is inherently bad, it just means that runners tend to have higher turnover of red blood cells than a sedentary person - and therefore need more iron!

How We Absorb Iron

Iron is mostly absorbed through our intestines (or through recycling iron from damaged red blood cells). We have a very tightly controlled absorption of iron because we want that optimal range. A hormone, called hepcidin, blocks the absorption of iron in the gut. This is really important in the context of exercise (especially for female athletes) because there are a few factors that increase hepcidin, which in turn makes it more challenging to absorb iron - even if we are eating or supplementing enough!

Hepcidin increases in response to inflammation. Exercise is a stress that increases inflammation in the short-term. This is a good thing and is necessary for adaptation improvement within the context of exercise. That said, it also impacts how we absorb iron (for up to a full day after!). Iron taken after a really intense training effort is not likely to be absorbed as well as iron taken on a rest day.

Hepcidin levels also vary throughout the day and throughout our menstrual cycle. They are lowest in the morning, and at the start of your cycle, when you have your period. Which makes sense biologically, we don’t want to block iron absorption while we are actively losing iron. 

How fuelling impacts Hepcidin

Even our energy intake within the context of exercise can influence how we absorb iron. When we train in a calorie deficit, our hepcidin increases. When we train in a calorie and carbohydrate deficit, hepcidin increases even more. Over many months of intense training in a deficit, you can imagine how chronically high hepcidin levels might significantly impact our ability to absorb iron.

Often we think of increasing protein intake to help with iron levels. This makes sense as many high-protein foods also have iron and athletes also often have a hard time getting enough protein for recovery and optimal performance. However, the importance of carbohydrates in our training is often forgotten or worse, carbohydrates are villanized. Many athletes are chronically under-fueling carbohydrates, as well as in calories (and sometimes protein!) in general.  When you combine this under-fuelling with high training loads and monthly menstruation, female endurance have can have a really challenging (or downright impossible) time reaching or maintaining enough iron. 

We can discuss optimal times to take our iron and increase iron-rich foods in the diet, but if we aren’t shifting our focus to optimizing our nutrition, we are missing a huge piece of the puzzle.

Curious about where to start? Book a meet and greet appointment with one of our naturopathic doctors to learn more.