Unsplash | Brian Suman

Drinking Cow's Milk Could Increase Chance Of Breast Cancer, Says New Study

Amy Pilkington 1 Mar 2020

Hey look, another study with more data about how something you love might be killing you!

Okay, I'm joking a little bit, but so many of the articles I read about this study either completely misunderstood the findings or were deliberately misleading.

So let's call this my small attempt to add some rationality to the news with a little help from a few experts.

So what about that headline, huh?

Giphy | The Little Vampire

The study from researchers at Loma Linda University Health did find an association between the amount of cow's milk women were drinking and the chance they had of developing breast cancer.

That is fact, but there are a few asterisks that just can't fit into the limited character count of a headline.

Load Comments

First, as with any study about a specific food or beverage, there are far too many variables to ever get a true control group.

Giphy

If it was possible to put an equal number of clones on the exact same diets, living the exact same life, except one group drank milk and the other didn't, maybe we could see some causation.

But since this is real life and ethics are a thing, all of these studies are about correlation not causation. The milk isn't causing the cancer, but it could be playing some role. Maybe.

Load Comments

That's why one week we'll see a study saying X food is good for us only to be told next week that it's killing us.

Giphy

This study did have a large sample size, which is good. They looked at 53,000 North American women over 30, all of whom were cancer-free at the beginning of the study.

They tracked various consumption habits of soy and diary products over eight years and by the end of the study, 1,057 of the women had been diagnosed with breast cancer.

There was no correlation found between the cancer risk of women who drank soy milk, but for the women who drank cow's milk, the correlation showed a steep increase in the risk that kept growing the more the women drank.

Load Comments

The numbers sound scary.

Giphy

First study author Gary E. Fraser, MBChB, PhD, said:

"Consuming as little as 1/4 to 1/3 cup of dairy milk per day was associated with an increased risk of breast cancer of 30%. By drinking up to one cup per day, the associated risk went up to 50%, and for those drinking two to three cups per day, the risk increased further to 70% to 80%."

Load Comments

At first glance, 80% for only two-to-three cups of milk per day is terrifying!

Giphy | The Late Late Show with James Corden

But if you stop and think for a moment it seems unlikely. People drink a lot of cow's milk and we're not all dropping dead of breast cancer.

That's because the percentage is increased risk, not actual risk.

Load Comments

I thought the explanation an assistant professor at Mount Saint Vincent University, Jennifer Brady gave to the CBC was a good one.

Giphy | Netflix Philippines

She helped put the numbers in perspective. Starting with 100 women is a good way to understand percentages.

If 100 women didn't drink milk, 2 of them would likely still get breast cancer. If all 100 began drinking one cup per day, according to the study you'd expect 50% more of them to get cancer.

Only 2 women got cancer the first time. Half of that is 1 woman, so with all 100 women drinking milk, a 50% increase in risk would just mean that 3 women would get cancer.

Load Comments

So in our 100 women, the risk of cancer went from 2% to 3%.

Giphy

When you put it that way, the study seems far less sensational, doesn't it? And far less newsworthy.

In fact, the 1,057 women who were diagnosed with breast cancer during the eight years of the study account for only 1.99% of the 53,000 women included.

So...average risk?

Load Comments

Where does that leave us?

Giphy

About where we started, which is the usual result of these sorts of studies.

The human diet, and humans in general, are so varied that singling out a specific food and trying to prove that it's objectively good or bad is pretty much impossible.

If you like diary, enjoy it. There are plenty of nutritional benefits. If you need or prefer alternative milk options, go for it! Anything can be bad if you have too much of it, so enjoy in moderation.

h/t: Science Daily, CBC

Load Comments
Next Article