At the Science Room (a community science group) Toby asked this question and it got me thinking. We all eat foods containing iron – I love spinach! And our blood is full of iron, but fridge magnets don’t stick to me?
Iron can be found in green vegetables like spinach and kale
Most things don’t really respond to magnets, but magnets are attracted to iron and it can sometimes be made into a magnet (ferromagnetic). Iron is also an important nutrient in people’s diets, because iron has some weird chemistry that makes it good at reacting with oxygen. Therefore we need iron to properly use oxygen (hence blood and meat’s rusty red colour).
Unfortunately for Toby, a number of things get in the way of his aim to be magnetic. The first is that iron is toxic if you have too much, as little as a quarter of a gram can poison a child. This is because excess iron can form deposits in protein and catalyse the formation of reactive oxygen compounds . Therefore the NHS’s recommended daily allowance for iron is only about 9mg per day and the “tolerable upper intake level” for iron is 45 milligrams per day.
Iron helps red blood cells transport oxygen
Due to this toxicity, there are less than 5 grams of iron in the average person. This is enough to see obvious magnetic effects…if all that iron was in one place. Instead the body’s iron is distributed to wherever energy is required. In addition, the body’s iron is bound to proteins on an atom by atom basis, with most iron in body bound to blood proteins. This reduces the magnetic impact of iron in the body, because to see strong magnetic effects you need lots of iron atoms next to each other, not spread through a large volume.
So it looks like you can’t survive consuming lots of iron and taking it into your body normally. But wait! What if you swallowed a piece of metallic iron? There are several reasons why this is a bad idea. The first is, if I was being very pedantic, the inside of your gut is considered to be outside the body by many biologists. So undigested stuff that’s in your gut (a lump of iron say) wouldn’t be considered part of your body. The second reason is that swallowing a solid, hard to digest object could lead to you blocking or injuring your gut. The third reason is there have been a number of injuries (and at least 1 death) caused by people swallowing magnets and metallic objects. Magnetic attraction can cause these objects to move: pressing on the gut wall, cutting off circulation and even tearing through tissue. So it’s probably a good thing that we don’t have concentrations of magnetic material in our bodies. If you know someone has swallowed a magnet, seek medical advice immediately.
Magnets attract iron filings producing patterns
Another reason it’s hard for humans (shout out to our robot readers) to become magnetic is only certain chemical forms of iron are strongly magnetic. Rust scrapings aren’t as magnetic as iron fillings because the iron in rust has reacted with oxygen and water. This removes some of the electrons that were orbiting the iron nucleus and giving iron its magnetic properties (oxidation). Iron in living things has had some of its outer electrons removed to enhance its ability to interact with other important chemicals (like oxygen and water), which is why many iron containing foods and supplements are not magnetic (go on, grab some spinach and try it). Some foods are fortified with iron filings, which are magnetic. However these generally are oxidised and dissolved by the digestive system soon after being eaten.
With a healthy iron intake, you will not be noticeably magnetic. Eating too much iron can make you very ill. It is possible to swallow magnetic material, but if you digest it, the magnetic effect is smaller, so arguably you don’t “eat” it. If you don’t digest it, it could cause death or serious injury. I’m sorry Toby, but spinach can’t make you magneto