Iron deficiency is a contributor to reduced performance in endurance sports such as triathlon, as it’s important that you get adequate iron to make haemoglobin, which is needed to transport oxygen to muscles in the red blood cells.
One of the reasons that athletes may become deficient in iron is that it’s poorly absorbed from food. Only 5-15% of the iron consumed in your diet will actually reach the blood stream. Iron from plant sources, such as green leafy vegetables, cereals and legumes, is more poorly absorbed than from animal sources such as beef, chicken and fish. This is largely due to compounds found in plants such as phytates and polyphenols, which are known to inhibit your iron absorption.
Single-meal laboratory studies have also found that drinking milk at the same time as eating food that contains iron does have an inhibitory effect due to the calcium and protein it contains, both known to reduce iron absorption. So, in theory, having milk on your cereal can actually reduce how much iron you will absorb.
However, studies that have looked at people’s overall diet over a period of time have found only a minimal effect on iron absorption from drinking milk.
Meeting your daily calcium requirements of 700mg is important for bone health, and drinking milk can play an important part in this, with 35% of your requirement coming from a 200ml glass. Non-dairy sources of calcium, such as soya, nuts and spinach, also contain iron-inhibiting phytates, so avoiding milk isn’t necessarily going to improve the amount of iron you absorb from food.
There are strategies you can use to try to improve your iron absorption: having a source of vitamin C at the same time as an iron-rich meal, such as a piece of fruit or some vegetables, can enhance your iron absorption. It’s also preferable to avoid drinking tea or coffee with these meals as they contain tannins, a type of polyphenol that’s known to inhibit iron absorption.
Drinking a glass of milk in the evenings, ideally around an hour before you go to bed, is actually a really good strategy to help you recover from a hard day’s training. The proteins in the milk will support muscle repair and growth, and the calcium content will support healthy bones.
So by all means, feel free to enjoy your evening glass of milk and continue to use it in smoothies and on cereal. Just try to avoid drinking that cup of milky tea or coffee with your iron-rich steak!