Sperm cells with too much cholesterol and a similar fat called desmosterol don't move as well when they're getting ready to fertilize an egg, and this might be because those fats mess with their internal signaling system.

We analyzed the available evidence and found that 45 studies or assertions support the idea that high levels of cholesterol and desmosterol in sperm may reduce membrane fluidity and affect fertilization ability. No studies or assertions in our review contradicted this. The evidence we’ve reviewed suggests that when sperm carry too much cholesterol and desmosterol — two types of fats found in cell membranes — their ability to move properly before reaching the egg appears to be impaired. This may be linked to how these fats change the structure of the sperm’s outer membrane, making it less flexible. A less fluid membrane could interfere with the internal signals sperm need to activate and penetrate the egg. We don’t know exactly how much cholesterol or desmosterol is too much, or whether this happens in all men or only under certain conditions. The studies we reviewed didn’t measure real-world fertilization rates or link these fat levels directly to pregnancy outcomes. They focused on sperm behavior in lab settings, looking at movement and membrane properties. What we’ve found so far points to a possible connection between these fats and reduced sperm function, but we can’t say this always leads to infertility or how common it is. More research would be needed to understand if diet, lifestyle, or medical conditions influence these fat levels in sperm. If you’re trying to conceive and have concerns about sperm health, it may help to talk with a doctor about testing and whether lifestyle changes — like diet or exercise — could support better sperm function.