Is cow’s milk healthy, or bad for your heart?

Whether it’s in tea or coffee, poured over cereal or by itself, many of us enjoy drinking cow’s milk every day.

But while it contains nutrients like calcium and protein, cow’s milk can also be high in saturated fat, which can raise cholesterol levels and, in turn, increase the risk of a heart attack or stroke.

That’s why the UK Government’s Eatwell Guide recommends choosing lower fat options like skimmed or semi-skimmed milk where possible.

However, in November, several UK media outlets reported on a new study that suggested drinking more than 1.5 glasses (300ml) of cow’s milk a day could raise the risk of a heart attack in women, regardless of how much fat the milk has.

Researchers in Sweden found that women who drank more than 4 glasses (800ml) of non-fermented milk a day had a 21 per cent higher chance of developing coronary heart disease, including having a heart attack, than those who drank around half a glass (100ml).

Meanwhile, women who drank 3 glasses (600ml) had a 12 per cent higher risk, while those who drank 2 glasses (400ml) had a 5 per cent higher risk, than those who only drank half a glass a day, according to the study published in the journal BMC Medicine.

The findings remained the same regardless of whether the milk was low-fat (0.5 per cent fat), medium-fat (1.5 per cent), or high-fat (3 per cent).

But the media reports largely failed to point out that the average person in the UK only drinks 177mls of cow’s milk a day (skimmed, semi-skimmed and whole milk) which is less than the 300ml the study found put women at higher risk of coronary heart disease.

The research followed nearly 60,000 Swedish women, who were 54 years-old on average, for an average of 30 years. It also looked at data on almost 41,000 men, who were 60 years-old on average and were followed for an average of 22 years.

None of the participants had coronary heart disease or had had a heart attack or angina (chest pain) at the start of the study.

However, unlike the women, no link between cow’s milk and a higher risk of coronary heart disease was seen for men.

The researchers also found that, for both women and men, drinking milk or yogurt that had been fermented with bacteria did not affect their risk of coronary heart disease.

What did the researchers say?

The researchers suggest that the risk of heart disease is higher in women because men’s bodies are better at digesting a sugar found in milk called lactose.

They explain that lactose can cause inflammation in the body if it’s not completely broken down.

The underlying mechanisms in the human body are not fully understood in the case of milk, but chemicals released because of chronic inflammation can lead to atherosclerosis, where fatty material (plaque) builds up inside blood vessels. This increases the risk of heart and circulatory diseases.

The researchers say fermented milk may not carry the same risk for women because it has been fermented with bacteria that reduces the amount of lactose in it.

What does other research say on the topic?

While this study found that women who drank more cow’s milk had a higher risk of heart disease, earlier studies have shown the opposite.

Research published in 2021 in the journal PLOS Medicine measured the levels of a specific type of fatty acid found in dairy in over 4,000 Swedish 60-year-old men and women’s blood.

They found those who had the highest blood levels of this fatty acid had a 30 per cent lower risk of developing coronary heart disease after 16.6 years than those who had the least.

This suggests that more research is needed into the relationship between dairy and heart health, and the impact milk has on the body.

How good was the research?

Although the researchers took participants’ age, weight and diet into account so they would not affect the results, the study was still observational.

That means we cannot conclude that drinking more milk directly causes a higher risk of heart disease for women.

A strength of the study was how large it was, with data from 100,775 people, including 59,988 women born between 1914 and 1948, and 40,777 men born between 1918 and 1952.

However, all the participants lived in a small area of Sweden, which means the findings may have been different in people from other places.

Finally, the data on how much milk people drank was collected by sending 3 questionnaires to the women in the study and 2 to the men, asking them to record the foods they had eaten over the last year.

This could affect the accuracy of the results, as people may have misremembered or mistaken how much milk they drank on average every day. 

How good was the media coverage?

The study was reported by many UK media outlets, including the Daily Express, the Daily Mail, the Daily Mirror and The Sun.

Overall, the reporting of the study was fairly accurate and pointed out that people may consume a lot of milk when they drink coffees such as lattes.

However, while all of them included the fact that people in the UK drink 1.2 litres of milk per week on average, only the Daily Express explained that this works out to around 177ml per day, which is less than the 300ml the study linked to an increased risk of coronary heart disease.

Many also reported that the researchers said lactose can damage cells and accelerate heart ageing.

But this is misleading, as the study only stated that lactose has been shown to cause the heart to age faster in mice and rats, not humans.

The BHF verdict

While we already know about the negative impact of saturated fat, more research is needed to confirm that drinking a lot of milk directly causes heart disease in women, and if opting for fermented milks could reduce that risk.

It’s also worth noting that the study only found women’s risk of coronary heart disease was higher when they drank more than 1.5 glasses (300ml) a day, and significantly higher when they drank more than 3 glasses (600ml).

For women in the UK, where the average intake is less than 200ml a day, enjoying a small amount of cow’s milk is unlikely to increase your chance of a heart attack or stroke.

But if you do often drink cow’s milk, try to swap full-fat products for skimmed or semi-skimmed versions to cut down on saturated fat.

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