Hi there, I'm one of the study authors. Iron plays many roles and is needed for your body to function correctly, but we found people who had higher blood iron levels because of their genes were getting diseases earlier in life and had a shorter lifespan, on average.

And what about people who have lower blood iron levels? Is lower better or worse than higher?

Generally better, but the answer is a little more nuanced.

We had access to data describing how DNA influences iron levels, and how DNA influences years of healthy life. This showed that the same DNA variations that change your levels of iron in the blood also change how many years you spend in good health.

Now, these genetic effects are relatively small, so we can confidently say that people who carry genes which cause them to have slightly lower iron levels (i.e. one standard deviation) than the population average will be healthier, on average.

However, extrapolating that further can be dangerous - for example, anyone with iron levels three standard deviations lower will not be three times healthier, they'd have no iron in their blood and be dead.

"Multivariate MR of iron-related traits on healthspan, parental lifespan, and longevity shows a protective effect for transferrin and a deleterious effect for serum iron."

not in life sciences too, and my interpretation of the above phrase is "if your body iron processing machine works well - good, if not - then bad" which i'd say would be pretty expected, and in general article sounds like there is positive correlation between well working iron related metabolism and longevity which seems not that surprising. They don't seem to address the machinery and nature of that correlation.

I think the article says iron levels are negatively correlated to longevity, but "the association might be due to a already-known correlation to haemochromatosis" which I have no idea what that is. I presume it's some known population that's old that happens to also have an enrichment of haemochromatosis but where individuals in that population without it do not show a positive defect in longevity?

Edit: specified as negatively correlated

Due to them saying that "the association might be due to an already-known correlation to haemochromatosis" I'm assuming they didn't have the data to correlate haemochromatosis to the data.

Haemochromatosis is a genetic disorder where individuals are unable to get rid of excess iron. If properly diagnosed, this is easily treatable with bloodletting (blood donation in this century :-)

Haemochromatosis is the sort of genetic disease that could really screw with data like this. Undiagnosed haemocromatosis leads to early death....so the correlation of excess iron to longevity should be treated as a weak piece of evidence until we can exclude people with the genetic disorder.

Great comment! For the iron - ageing link, we used two pieces of data: the effect of DNA on blood iron levels, and the effect of DNA on how long and healthy you live. We found the mutation that causes hereditary haemochromatosis had a large effect on early death (as expected). However, other genetic variations that increased blood iron levels also had a proportional effect on early death. So it looks like it is higher iron levels, not just haemochromatosis, that may accelerate the rate of ageing.

does this boil down to "diets that are high in iron, aka meat, will yield a life that is less long compared to a diet that is low in iron (meatless)?"

Is there any evidence that eating more meat actually causes higher blood iron levels?

Can someone answer the first question before we introduce a sixth?

"Too much" iron is by definition bad.

"too much" implies that it is bad; otherwise, it wouldn't be too much.

Correlation does not imply causation.

As a general rule, too much of anything is bad.

> is this saying too much iron is good or bad?

No, it's saying neither. The submission title could be seen as misleading.

"association" = misleading?