Eggs are not a cause of stroke: New study completely contradicts large meta-analysis in British Medical Journal and could be misleading to public
An observational study which claimed that eggs are linked to a rare type of stroke – called haemorrhagic stroke – should be treated with caution because it contradicts other studies, particularly a large meta-analysis in the British Medical Journal which found that eggs lowered the risk of haemorrhagic stroke by 25%.
Observational studies collect data from thousands of people but don’t control for any behaviours, unlike gold standard randomised controlled trials. This means they cannot be used to establish cause and effect. This is widely acknowledged by expert bodies who need evidence of mechanisms and direct effects before accepting that a food causes, or protects against, a disease.
The current study, published in the European Heart Journal, asked about the diets of more than 400,000 Europeans using questionnaires, then followed them up nearly 13 years later without any intervention or further dietary assessment. Eggs were not related to ischaemic stroke – which represents around 85% of strokes – but there was a small statistical association with the rarer haemorrhagic stroke.
Dietitian, Dr Carrie Ruxton comments: “We need to be clear that observational studies tell us nothing about cause and effect – they are rather like fishing expeditions that need to be followed up with controlled types of studies, such as intervention trials and mechanistic studies. It’s usual when analysing thousands of variables that some will throw up random statistically significant results, but that isn’t enough for public bodies to act.
“In this particular study, egg consumption was generally low – only around a third of an egg per day which equates to 22 kcal and 1½ grams of fat. Stroke sufferers ate only 1-2 grams more eggs per day than people who didn’t have a stroke. There is no way that such a miniscule difference could have been responsible for an increase in stroke and we need to get real about these types of findings to avoid confusing the public!
“Eggs are a low cost, high protein, vitamin-rich food for millions of people. Saying they cause stroke – without any good evidence – is highly misleading and will not help to protect people from strokes which are largely related to high blood pressure, salt intake, smoking, obesity and a lack of fruit and vegetables”.
- All UK health and heart advisory bodies, including the Department of Health and the British Heart Foundation, currently advise that dietary cholesterol from foods such as eggs does not increase the risk of heart disease for most people. Previous limits on egg consumption were lifted in the UK more than ten years ago.
- Egg consumption in the study was 16 grams a day on average amongst people who developed a haemorrhagic stroke and 14 grams per day on average in those who didn’t. Average egg intake across all people studied was < 1/3 of an egg per day.
- Those developing strokes were more likely to report heavy current smoking, less likely to report having vocational or university education, were generally less active, more likely to be unemployed, more likely to have a history of diabetes or hypertension, and were in a higher proportion from Northern Europe (Denmark, Norway, Sweden).