In Iran, women who drink skim milk or eat low-fat yogurt may be less likely to get breast cancer, but those who eat full-fat cheese or cream might be more likely—so the fat in dairy could be what makes the difference.

Iranian women who drink more milk are about 76% more likely to get breast cancer than those who don’t, even when you account for other dairy like cheese or yogurt—so milk itself might be doing something unique that raises risk.

Iranian women who eat more low-fat dairy like milk and yogurt seem to have a much lower chance of getting breast cancer compared to those who eat very little — it’s not proven to cause the protection, but there’s a strong link.

Iranian women who eat a lot of full-fat dairy like cheese and butter may be nearly 9 times more likely to get breast cancer than those who eat very little of it — but this doesn’t prove the dairy causes the cancer, just that they tend to happen together.

If you’ve had breast cancer and eat a lot of full-fat dairy like whole milk or cheese every day, you might be more likely to die from breast cancer than if you eat only a little — possibly because the fat in dairy affects hormones that help cancer grow.

If you’ve had breast cancer, eating a lot of full-fat dairy like whole milk, cheese, or butter might make you more likely to die from any cause — including things other than cancer — compared to eating only small amounts.