Moderate dairy consumption may help heart health

Wednesday September 12 2018

"Drinking three glasses of whole milk a day can help you live longer," reports the Sun.

An international team of researchers looked at dairy consumption among more than 136,000 people in 21 countries worldwide.

They found people who had more than 2 servings of dairy products a day were 16% less likely to die or have a heart attack or stroke during an average of 9 years of follow-up.

On the surface, this would seem to contradict UK advice to limit consumption of dairy products, especially full-fat products, as they're a rich source of saturated fat, which has been linked to heart disease risk.

But the study isn't a green light to eat as much cheese as you want.

Most of the benefit seemed to come from milk and yoghurt, and the effect was strongest in low and middle-income countries, where dairy consumption is generally much lower than the UK.

The question of whether benefits come from low-fat or full-fat dairy products wasn't conclusively answered in the study.

The benefits of full-fat dairy seemed greater. But in many parts of the world, low-fat dairy products are unusual or unavailable, which could complicate this finding.

And in some countries, it could be the case that many participants were eating healthy levels of saturated fats.

The same isn't true of most adults in the UK, who eat more than the recommended level of saturated fats – no more than 10% of your calorie intake should come from saturated fats.

The UK guidelines to consume 2 to 3 portions of dairy products daily, and choose reduced-fat versions, remain unchanged.

Where did the story come from?

The large team of researchers came from 32 institutions, from countries including India, Canada, Pakistan, South Africa, Brazil, Colombia, Zimbabwe, Saudi Arabia, Iran, Turkey, Chile, Poland, Sweden, Malaysia, the Philippines, United Arab Emirates, Argentina, the US, China and Bangladesh.

The study was funded by grants from many of these countries' health ministries and research institutes, as well as pharmaceutical companies.

It was published in the peer-reviewed The Lancet.

The study got widespread attention in the UK media. The Sun said the findings were "flying in the face of current medical advice" on choosing skimmed milk, while the Mail Online incorrectly stated that "a knob of butter every day" would lower the risk of heart disease. The study found no evidence that butter was beneficial for heart health.

And many UK media sources didn't explain that the results may only be relevant for people living in low- and middle-income countries, where dairy intake is usually much lower than for people living in the West.

The Guardian's headline, "Dairy food in moderation may protect the heart", is probably the most accurate summary.

What kind of research was this?

This was a cohort study of people aged 35 to 70 years, from 21 countries across 5 continents.

Observational studies like this are good for showing patterns – in this case, the link between dairy product consumption and cardiovascular disease or death – but can't show that one thing directly causes another.

Other unmeasured factors could affect the results.

What did the research involve?

Researchers recruited volunteers to complete food frequency questionnaires tailored to their local region, which asked them how often they ate a wide range of foods.

The 136,384 people whose questionnaires were filled in correctly, and who didn't have cardiovascular disease already, were followed up for an average of 9.1 years.

Researchers recorded whether people died or had a heart attack, stroke or heart failure during follow-up. They then looked at whether people eating different amounts of dairy products, and different types of products, had differing risks.

The researchers took account of potential confounding factors, including:

  • age
  • sex
  • education
  • whether they lived in urban or rural places
  • smoking status
  • physical activity
  • diabetes
  • family history of cardiovascular disease or cancer
  • how much fruit, vegetables, red meat and starchy foods they ate

Areas like China, south and southeast Asia, and Africa have relatively low rates of dairy product consumption, while Europe, North and South America and the Middle East have relatively high consumption.

Because of this, researchers looked at whether the links between dairy and death or cardiovascular disease varied by region.

What were the basic results?

Overall, researchers found eating more than 2 daily portions of dairy products was linked to a 16% reduction in risk of either a heart attack, stroke, heart failure or death from cardiovascular disease, compared with eating no dairy (hazard ratio (HR) 0.84, 95% confidence interval (CI) 0.75 to 0.94).

Any of these outcomes occurred in 5.8% of people eating more than 2 daily portions compared to 8.7% of people eating no dairy. The results for total dairy consumption seemed to be driven by consumption of milk and yoghurt.

People who drank more than 1 glass of milk a day had a 10% reduction in risk (HR 0.90, 95% CI 0.82 to 0.99) and those who ate more than 1 cup of yoghurt a day had a 14% reduction in risk (HR 0.86, 95% CI 0.75 to 0.99).

There was no link between consumption of cheese or butter and risk.

The benefit was stronger for people consuming whole fat dairy products only (HR 0.71, 95% CI 0.6 to 0.83) than for people consuming whole- and reduced-fat dairy (HR 0.84, 95% CI 0.68 to 1.03), but the reason for this is unclear.

How did the researchers interpret the results?

The researchers said: “Our study suggests that consumption of dairy products should not be discouraged and perhaps should even be encouraged in low-income and middle-income countries where dairy consumption is low.”

Conclusion

This study is interesting because of its size and the international reach of its coverage. Few studies have looked at dairy consumption and cardiovascular disease in such a wide range of countries, including those where dairy consumption is relatively low. It's interesting to see confirmation that dairy products in moderation seem to be beneficial for heart health for people in most regions of the world.

However, the key word is moderation. A portion of dairy products in the study was defined as a 244g glass of milk, a 244g cup of yoghurt, a 15g slice of cheese or a 5g teaspoon of butter.

Limitations of the study included:

  • its observational nature, which means it cannot prove cause and effect
  • researchers measured people's dietary intake only once at the start of the study, so we don't know if they changed their diet habits
  • the people in the study were quite young, so 9 years is a short period to see whether they were likely to die or have heart attacks or strokes

The role of low fat or full fat dairy products is not clear from this study, partly because low fat dairy products are uncommon in many of the countries where the study took place.

Current UK guidelines recommend:

  • the average man aged 19 to 64 years should eat no more than 30g of saturated fat a day
  • the average woman aged 19 to 64 years should eat no more than 20g of saturated fat a day

Based on this research, it may be the case that dairy products are a good source of saturated fats as long as you do not exceed the recommended limits.

The problem is that most of us in the UK eat far more saturated fats than this. So we should follow recommendations, such as those from the British Heart Foundation, to opt-for reduced fat dairy products.

Analysis by Bazian
Edited by NHS Website