Thursday August 1 2013
Iron can be found in foods such as red meat, nuts and raisins
"Iron-rich foods such as steak…could cut the risk of dementia in later life, say researchers" is the misleading claim in the Daily Mail. The Daily Telegraph follows suit, stating that scientists claim we should "Eat steak to reduce risk of dementia".
But the cohort study that both papers seized on did not actually look directly at diet. The study followed more than 2,550 older adults for over a decade and found that those who had anaemia at the start of the study were more likely to go on to develop dementia.
Anaemia is caused by reduced levels of either red blood cells or the oxygen-carrying pigment in red blood cells called haemoglobin, and has a wide range of potential causes.
As well as diet-related causes, stomach ulcers, chronic kidney disease, inflammatory bowel disease or, in some cases, a general poor state of health are all associated with anaemia.
Both papers' reporting and narrow focus on diet is based on a simplistic view of anaemia and is not supported by the study's results.
Overall, this study does suggest a link between anaemia, general poor health and dementia. But whether anaemia directly causes an increase in dementia risk is difficult to tease out.
More studies are therefore needed to determine whether a preventative strategy that just targets anaemia could effectively reduce the risk of dementia, or whether a more wide-ranging strategy is needed.
Where did the story come from?
The study was carried out by researchers from Ajou University School of Medicine in South Korea and other research centres in the US. It was funded by the US National Institute of Aging, National Institutes of Health, and the American Health Assistance Foundation.
It was published in the peer-reviewed medical journal Neurology.
Both the Daily Mail and The Daily Telegraph extrapolated the study's results to suggest that iron-rich foods can delay the onset of dementia. They also both suggest in their headlines that the researchers in the study advise people to eat iron-rich foods to prevent dementia.
However, the study did not look at people's diets or assess the impact of changing diet, and doesn't make recommendations about diet based on their findings.
As the researchers make clear in their conclusion, "The implications of these findings for dementia prevention are not clear".
Eating iron-rich foods does reduce the risk of iron deficiency anaemia and, in some cases, helps combat iron deficiency anaemia in those who have the condition.
However, this study looked at all types of anaemia, not just anaemia caused by iron deficiency. We therefore can't be certain that this would reduce the risk of dementia.
What kind of research was this?
This was a prospective cohort study looking at whether anaemia in older adults could be a risk factor for dementia.
The researchers say that some studies have suggested a link, but these studies have generally:
- been cross-sectional (where information is taken at just one point in time)
- only followed people up for a short period of time
- only included very select groups of people or did not take into account some factors that could account for a link (potential confounders)
They therefore wanted to carry out a study that would avoid these limitations and give more robust results.
What did the research involve?
The current research was part of the ongoing US Health, Aging and Body Composition (Health ABC) study, which started in 1997 by enrolling more than 3,000 older adults aged 70-79.
The researchers identified which participants had anaemia and followed them up over time to see if they were more likely to develop dementia.
They took blood samples from the participants in the third year of the study and used accepted World Health Organization criteria to identify those with all types of anaemia. They identified whether they carried a particular form of the ApoE gene, which is associated with an increased Alzheimer's risk.
The participants also provided information on their sociodemographic characteristics and medical history, including what medications they were taking.
The researchers had this data for 2,552 participants (average age 76) and followed them up for an average of 11 years. They assessed participants' cognitive function roughly every two years using a standard test.
Dementia cases were defined as those where there was a specified decline in performance on the cognitive test, if the participant started taking medication for dementia, or if they were recorded as having dementia in their hospital records.
What were the basic results?
About 15% of participants had anaemia in year three of the study. These people were more likely to be older, carry the form of the ApoE gene associated with increased Alzheimer's risk, have less education and lower literacy, and have a history of diabetes, high blood pressure or heart attack.
More participants with anaemia (23%) went on to develop dementia than those who did not have anaemia (17%). After taking confounders into account, those with anaemia of any cause were still about 49% more likely to develop dementia compared with those without anaemia (hazard ratio 1.49, 95% confidence interval 1.11 to 2.00).
How did the researchers interpret the results?
The researchers concluded that anaemia is associated with an increased risk of developing dementia in older adults.
They say that further studies looking at why anaemia might be associated with dementia would help determine whether strategies to prevent dementia should target anaemia specifically, or if they should focus on improving general health.
This study found that older adults aged 70-79 with anaemia are more likely to develop dementia over the course of a decade than those without the condition.
The study has a number of strengths, including its relatively large size, the fact that the sample was varied in ethnicity and gender, and that the participants were assessed regularly and followed up over a long period of time.
However, the people in the study who had anaemia also had a number of other features that would increase their likelihood of developing dementia. For example, they were older and more likely to have cardiovascular disease, which is associated with one form of dementia (vascular dementia), as well as more likely to have a genetic risk factor for another form of dementia (Alzheimer's disease).
It is not known how long the participants had anaemia as only one blood test was performed. It is also not known what type of anaemia they had and whether or not they were receiving treatment. Although the researchers did try to take all of this into account in their analysis, these and other factors may still have had an effect.
The other main limitation of this study was that it did not carry out the very detailed standard analyses that would be used to diagnose the various different types of dementia.
Instead, they relied on identifying diagnoses in people's medical records, whether their physicians prescribed them medication for dementia, or if there was a reduction in their performance on cognitive testing.
This may mean that some cases could be missed or some people considered to have dementia might not have the condition when investigated further.
The researchers point out that anaemia itself can cause lower levels of oxygen in the brain, resulting in poorer cognitive function. This may have mimicked dementia on cognitive testing.
Overall, this is a useful study that does suggest a link between anaemia, general poor health and dementia. This is a link that deserves further investigation.
However, it is currently far too early to state that eating iron-rich foods or taking iron supplements can reduce the risk of dementia.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.