"Eating cheese does not raise risk of heart attack or stroke," reports The Guardian. This follows a large review pooling the results of 29 observational studies into the link between dairy consumption and cardiovascular disease; coronary heart disease, as well as all-cause deaths.
The studies included almost 1 million people from around the world and found no increased risk of the factors mentioned related to dairy consumption. They even found a very slightly lowered risk (2%) of cardiovascular disease and all-cause death from eating fermented dairy products such as cheese.
Dairy products are often high in saturated fat, something we should consume small quantities of, as it is linked to increased risk in health outcomes such as heart attacks and stroke. However, they are also high in calcium (which helps strengthen bones), a good source of protein and part of a balanced diet.
In April, the National Osteoporosis Society issued a warning that the perception of dairy products as unhealthy could lead to an increase in osteoporosis cases in the future.
The daily guideline amount of saturated fat is no more than 30g for the average man and 20g for the average woman. If you are concerned about consuming too much saturated fat, opt for low-fat versions of yoghurt, milk, cheese and other dairy products.
If you are vegan you will need to take steps to ensure you get enough calcium in your diet. Read more diet advice for vegans.
Where did the story come from?
The study was carried out by researchers from Reading University, UK, University of Copenhagen, Denmark and Wageningen University and Research Centre, The Netherlands.
The study was funded by an unrestricted grant from the Global Dairy Platform, Dairy Research Institute and Dairy Australia. However, the funders are reported to have had no role in the study design or any other study processes. The researchers declared receiving funding from various dairy and food companies as well as one author being a member of advisory boards for a number of large food companies.
The Guardian's reporting of the study was accurate, highlighting that dairy products are an important source of calcium, but are often high in saturated fat – something we should not be consuming too much of.
What kind of research was this?
This was a systematic review which aimed to identify and pool the results of cohort studies that have looked at the links between dairy consumption and health outcomes including cardiovascular disease, stroke and death.
A systematic review is a good way of summarising research in a particular area. Cohort studies are often the best available evidence when looking at whether something such as diet has an effect on long-term health outcomes. However, you can never rule out the possibility that other health and lifestyle factors (confounders) are influencing the results.
Randomised controlled trials, which are seen as the best way to assess evidence, are often hard to conduct: it may be difficult (and often unethical) to randomly assign enough people to dietary patterns and follow them for long enough to observe health outcomes.
What did the research involve?
The authors searched literature databases for prospective cohort studies published up to September 2016. Eligible studies had included a group of healthy adults (>18) and followed them over time to look at the amount of dairy they consumed and incidence of cardiovascular disease, coronary heart disease and death from all causes.
A total of 29 studies involving 783,989 participants were included. Participants had an average age of 57 years, an average BMI of 25.4, and were followed up over time between 5 and 25 years. The majority of studies (17) came from Europe with others from Asia, Australia, and the US.
Portion sizes were standardised and researchers looked at the link for each increasing increment per day:
- 244g a day for milk
- 50g a day for yoghurt
- 20g a day for fermented dairy products (including cheese, yoghurt and soured milk products)
- 10g a day for cheese
- 200g a day for total, high-fat and low-fat dairy
The researchers adjusted their analyses for the following confounding variables:
- alcohol intake
- body mass index (BMI)
- reported physical activity
- food energy intake
They also took study quality into account.
What were the basic results?
There were a total of 93,158 deaths, 28,419 incidences of coronary heart disease and 25,416 incidences of cardiovascular disease.
Total dairy intake (either high-fat or low-fat), milk intake and yogurt intake were not associated with risk of all-cause death, coronary heart disease or cardiovascular disease.
Cheese (per 10g/day) was not linked with risk of death or coronary heart disease. There was the suggestion of a reduced risk of cardiovascular disease, but this was on the threshold of statistical significance so may just be a chance finding (relative risk [RR] 0.98, 95% confidence interval [CI] 0.95 to 1.00).
Total fermented dairy intake (per 20g/day) was associated with 2% lower risk of both death and cardiovascular risk in a link that just reached statistical significance (RR 0.98, 95% CI 0.97 to 0.99). However, in sensitivity analysis (an analysis of potential uncertainty), excluding a Swedish study of women's results for cheese, there was no longer a significant link.
How did the researchers interpret the results?
The researchers concluded that "this meta-analysis combining data from 29 prospective cohort studies showed there were no associations between total dairy, high- and low-fat dairy, milk and the health outcomes including all-cause mortality, coronary heart disease or cardiovascular disease. The modest inverse associations of total fermented dairy were found with all-cause mortality and cardiovascular disease, but not coronary heart disease. By examining different types of fermented food in relation to CVD, we found marginally inverse association with cheese but not yogurt."
This large meta-analysis of cohort studies demonstrated no increased risk to cardiovascular disease, coronary heart disease or all-cause death from eating dairy products.
The review has strengths in its large size and the fact it was able to analyse different types of dairy product, such as high and low-fat and everyday products such as cheese and yoghurt.
However, there are a number of factors to consider:
- The results of a systematic review are only as good as the quality of the underlying studies. These are all observational studies and it's possible that unadjusted health and lifestyle factors are having an influence. Different studies adjusted for different variables; for example, some adjusted for overall diet, smoking and total energy intake, others did not.
- Studies may also have differed in how accurately they measured analysed dairy intake and health outcomes. This may explain some variation in individual study results, and make it difficult to summarise these studies all together.
- Overall there wasn't good evidence for any link between dairy and these health outcomes. The lowered risk of cheese fell short of statistical significance. The links between fermented products and all-cause death and cardiovascular disease were down to the results of one study. This shows the influence that one study, which may differ in methods from others, can have on the overall results.
- There are other dairy products such as cream that are very high in fat but were not individually assessed and might have had a more negative effect on health.
- Only three studies were from Asia, compared to 17 from Europe. The results might therefore be more generalisable to European populations than the rest of the world.
Dairy products such as cheese, milk and butter often contain high levels of saturated fat and salt, particularly the full-fat versions.
Consuming too much saturated fat or salt is known to be bad for us and can increase risk of health outcomes such as cardiovascular disease. However, dairy is also an important source of calcium and consuming it in moderation is part of a balanced diet.
Unless you choose not to eat dairy products as you are a vegan, or due to allergies or intolerances, there is no clinical need to cut an entire food group, like dairy, from your daily diet.
As Aristotle famously said, "everything in moderation". And this is usually a good rule to live by when it comes to healthy eating.