Updated: Mar 20, 2021
Are you an endurance athlete? Are you female? Are you a long distance runner? Do you play high impact sports? Do you have a high sweat rate or suffer from the occasional GI problems?
If any of the above applies to you, let's start by testing your knowledge about iron and blood, and the connection between the two.
Did you know that...
In sedentary people, red blood cells can live up to 120 days
In endurance athletes, red blood cells turnover is about 70 days
Females on average need 18 mg of iron daily but males on average need only 8-10 mg per day
Vegetarians and vegans should have 1.8x more iron than average
You can lose about 2 mg of iron per one litre of sweat
Meat sources of (heme) iron is more bioavailable than plant-based sources (non-heme)
Most healthy adults (including athletes!) can meet all iron needs through a well-balanced diet without supplementation.
Why is iron important? Iron is essential for our health because we need it to make blood. An average adult has about 3 to 4 grams of iron in the body. 60-70% of iron is found in hemoglobin in red blood cells, the rest is found in myoglobin in our muscles, or stored as ferritin and hemosiderin in our liver, spleen, and bone marrow. There is also a small amount in transit and being transported by transferrin through the blood plasma.
Whilst not the focus of this blog, iron is also extremely important for brain development, neurological functions and immunity - which explains why pregnant women, children and adolescents need to get enough iron.
Iron for Athletes Iron is important for athletes because it provides oxygen for respiration and energy production for aerobic exercises. Our athletic performance is very much dependent on the capacity of two iron-containing proteins: hemoglobin and myoglobin.
Hemoglobin in red blood cells transports oxygen from our lungs to our muscles. Myoglobin in the muscles receives the oxygen from the red blood cells and transports it to the mitochondria, where the oxygen is used for respiration and energy production.
Why do endurance athletes need more iron? This is because endurance athletes undergo higher volume of aerobic training that demands oxygen transportation. Higher impact from running increases rupture of red blood cells (hemolysis) and requires more iron. A quicker RBC turnover means that athletes need to replenish iron stores more quickly from a high quality diet to support red blood cell production (erythropoiesis). Endurance athletes recycle their RBC faster because they are prone to
Greater sweat loss from longer exercise and higher body temperature
Small amounts of gastrointestinal bleeding, which is common in runners
Rupture of red blood cells (hemolysis) from the impact of running. This also applies to high impact sports like football, basketball and rugby.
How much iron do we need? The recommended daily allowance (RDA) for adults 19-50 years is as follows
Male - 8 mg per day
Female - 18 mg per day
Pregnancy - 27 mg per day
Lactation - 9 mg per day
The requirements are higher for women due to blood loss through menstruation and for pregnant women because they need extra blood circulation for the growing fetus. The RDAs for vegetarians are 1.8 times higher because plant-based sources of iron are non-heme and less bioavailable. Vegetarians need to compensate with quantity. If you don't think you are getting enough iron, below are some tips to improve iron absorption. Avoid taking iron supplement because chronic supplementation can increase the risk of iron overload, UNLESS you have a prescription from your doctor. Dietary Iron Dietary iron can come in two forms - heme and non-heme.
Heme iron is more bioavailable and easily absorbed (15-25%) . Sources include (per 100g)
Organ meats such as beef liver (6.5mg)
Meat such as beef steak (3.7mg)
Shellfish such as oysters (7.3mg), mussels and clams (2.8mg)
Poultry such as dark turkey meat (1.4mg)
Fish and seafood such as canned sardines and canned tuna ( 1.7mg)
Non-heme iron is less bioavailable and less easily absorbed (2-20%). All plant based foods, fortified foods and supplement sources are non-heme. Examples:
Beets, dandelion, kale, dark leafy greens, spinach (2.4mg)
Legumes such as beans, lentils (1.5mg)
Dark chocolate (2.7mg per 35g serving)
Nuts and seeds, such as pumpkin seeds (2.7mg per 1/4 cup)
Dried fruits such as raisins, apricots (2.7mg)
Egg yolk (0.5mg per egg)
Fortified cereals and grains
Bioavailability of Iron The bioavailability of iron is about 14-18% from mixed diets that include meat and seafood, compared to 5%-12% from vegetarian diets. Why are the numbers so low? Iron absorption is limited because our body has no physiological mechanism to remove excess iron. The level of iron in our body is tightly regulated by the hormone hepcidin, which controls iron absorption, iron stores and distribution throughout the body.
Several Factors Can Affect Iron Absorption
Iron status (e.g. iron stores) and health status (obesity).
The source of dietary iron - heme from meat vs non-heme from plants.
Use of medication such as proton pump inhibitor or omeprazole can reduce stomach acidity and therefore lower iron absorption.
Gastrointestinal health. Since iron absorption takes place in the small intestines, iron-deficiency (ID) and iron deficiency anemia (IDA) very often start with issues in the gastrointestinal tracts. Inflammatory bowel diseases (IBD) is one of the most notable GI conditions associated with IDA. The main factors that can cause ID/IDA are chronic GI bleeding, malabsorption and inflammation.
Intake of calcium can reduce the absorption of iron (both heme and non-heme) due to mineral-mineral interactions. And vice versa.
Antinutrients can inhibit iron absorption. Examples include (1) tannins in coffee, tea, wine and berries (2) phytates or phytic acid in legumes such as beans, peas and lentils, (3) phosphates in carbonated drinks, e.g. soft drinks and beer, and (4) polyphenols in cereal legumes and spinach.
How To Improve Iron Absorption
Avoid drinking tea, coffee and red wines when consuming iron-rich foods
Avoid consuming milk or dairy when consuming iron-rich foods
Vitamin C can help absorption of iron, e.g. add lemon juice to your food
Cook with iron wok, cast iron grill or iron utensils.
Iron Deficiency (ID) Iron deficiency alone does not mean anemia. This is because iron deficiency occurs in stages. It starts with (1) depleting iron stores, followed by (2) greater depletion and iron deficiency erythropoiesis (red blood cell production), and (3) eventually iron deficiency anemia (IDA). If you feel fatigue, low energy or difficulty concentrating, you may be low on iron but it can equally be due to lack of sleep, dehydration , overtraining or many other factors.
Iron Deficiency Anemia (IDA) When iron deficiency anemia (IDA) happens, there is not enough red blood cells or hemoglobin in the blood and lower hematocrit (lower proportion of red blood cells in the blood by volume). Several types of blood test can be used to identify IDA, including hemoglobin levels, serum ferritin, transferrin saturation (TSAT), as well as blood count. Symptoms of IDA include fatigue, weakness, confusion, difficulty concentrating, sensitivity to cold, pale skin, hair loss, brittle nails, impaired cognitive function, immune function or athlete performance.
The World Health Organization defines anaemia as a haemoglobin (Hb) concentration below 13 g/dl in men over 15 years of age, below 12 g/dl in non-pregnant women over 15 years of age, and below 11 g/dl in pregnant women.
If you are worried about your iron levels, consult your doctor and get some tests (e.g. ferritin levels). Most of us can easily increase our iron intake through diet. Note that iron-deficiency anemia is uncommon. People who have iron deficiency or IDA usually suffer from other nutrient deficiencies or more serious health conditions. Treatment can involve short term oral supplementation, and in more serious cases, intravenous supplementation or blood transfusions carried out by medical professionals. I know I sound like a broken record: for most of us, a balanced nutrition is all we need to meet our iron requirements!
Elites or endurance athletes may sometimes have lower hematocrit (Ht, HCT), which is the percentage of red blood cells in blood by volume. A low hematocrit is sometimes called sports anemia.
Before you get worried, sports anemia is not anemia, and is only a temporary condition. In fact, athletes usually have a greater mass of red blood cells and hemoglobin compared to sedentary people. When athletes undergo intensive training, their blood PLASMA volume increases rapidly but the amount of iron increases at a slower rate. This causes the concentration of hemoglobin in the blood to fall temporarily.
The "problem" of lower hematocrit usually goes away after several weeks when the production of new red blood cell and hemoglobin catches up with the higher training load. Meanwhile, athletes can modify their diet with iron-rich foods and short-term supplementation to meet the demands of more intense training.
Endurance Athletes Have Younger Red Blood Cells
Whilst exercise does stimulate red blood cell production, the higher red blood cell mass is somewhat offset by more ruptures of red blood cells during muscle contractions and foot strikes during intense exercise. Consequently the average age of the red blood cells in endurance athletes are lower at about 70 days, versus 120 days in sedentary people. The upside is that the new and younger red blood cells have improved oxygen carrying capacity for aerobic exercises, hence improved athletic performance.
Who Else Need More Iron? Below are the groups who are at higher risk of iron deficiency.
Endurance athletes (heavy sweat loss, runners with pavement pounding, GI bleeding)
Females with heavy periods
Females who are pregnant or lactating
Vegetarians and vegans
Frequent blood donors
People with chronic kidney failure
Any combination of the above
Athletes tend to be higher risk for iron deficiency
Athletes are more likely to have iron deficiency due to insufficient iron intake as some may be following a restricted diet to make weight or body composition in preparation for a competition. Athletes who prefer plant-based diets should pay attention to improve iron absorption given plant sources are non-heme iron, and plants also contain antinutrients and enzyme inhibitors. Some athletes may lose more iron through higher sweat rates, GI bleeding, hemolysis (pavement pounding) and myoglobinuria (loss of blood through urine). Risks of Iron overload Excessive intakes can cause gastrointestinal problems, nausea, abdominal pain, vomiting and faintness. Overdoses can be fatal because the body cannot remove the excess iron easily. People with hemochromatosis (a rare hereditary condition) or liver disease may have a risk of excessive build up of iron. For most healthy adults with normal intestinal function, there is little risk of iron overload from dietary sources.
Eat Real Food If you are an endurance athlete, a female runner who pounds the pavement and sweats a lot (like me!), I hope the above can help improve your iron intake and absorption. There is no need for supplements because you can absolutely meet your requirements with a well balanced diet.
Eat real food - which you do anyway, is far more enjoyable and pleasurable!
Interested Health Coaching?
Hope you enjoy the above. If you want to dig deeper into the topic or if you are interested in improving your nutrition, overall well-being or holistic health coaching please get in touch for a free 30 minutes consultation. References
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