Dementia is a hot topic for researchers because of the enormous burden it has both on our personal lives and societies as a whole. Screening and diagnosis of dementia has improved over the last few years, but we still have controversies and much uncertainty about the best way to treat the disease. Also, due to the rapidly ageing population, there is now a great need for researchers to focus on how to prevent dementia.
We do not know much about the direct causes of dementia, but the evidence for possible causal associations includes (Prince et al., World Alzheimer Report 2015):
- Low education
Knowing the risk factors and acting upon the modifiable ones can lower the incidence of the disease. Our level of education is one of the most accepted risk factors in epidemiological studies for dementia. This factor is a modifiable one, so knowing more about how it influences the disease and acting upon it can lead to lower incidence levels and improved quality of life.
An explorative meta-analysis was conducted in order to find out whether a dose-response relation exists between education and dementia risk (Xu et al, 2015).
A systematic search on PubMed, EMBASE and the Cochrane Database of Systematic Reviews was conducted using the keywords dementia, Alzheimer’s disease, mild cognitive impairment, multi-infarct dementia, vascular dementia, school, education and educational.
For studies to be included in the final analysis they had to fulfil the following criteria:
- Report original data concerning relative risk of dementia (including all dementias) with low or high education using a longitudinal cohort study
- The study population is representative of the general population
- Educational attainment is categorised into at least three levels
Studies were included in the dose-response meta-analysis if there was available data about case number and person-years with different educational categories.
Studies were excluded if they:
- Reported no new data
- Failed to report prospective associations between education and dementia incidence
- The variables of educational levels were continuous or dichotomous
- Were case-control or cross-sectional
- Explored non-epidemiological associations of education with dementia
- Had no concrete case number or person-years data in accordance with different educational levels
- Explored influences on cognition, dementia progression or age at onset
- Had the same population or were a replica study
- Explored associations between socioeconomic status and dementia, parental education and educational quality or explored early-onset dementia.
A random-effects meta-analysis was performed to estimate pooled relative risk (RR) of dementia and 95% CIs weighted by the inverse variance method. First, estimates of the highest exposure level (which is the lowest category for low education and the highest category for high education) were pooled against the reference level to derive an overall relative risk which is regarded as the pooled effect of the high dose exposure, independent of the cut off value used in studies. And then, estimates of the second lowest exposure level (which is the second highest category for low education and the second lowest category for high education) were pooled against the reference level to derive an overall relative risk, which is regarded as the overall effect of the low dose exposure, independent of the cut off values used in studies. The two relative risk values were compared in order to examine whether a trend of dose-response relation between dementia and educational level existed.
A dose-response meta-analysis using generalised least square regression was conducted in order to assess the pooled dose-response relation between low/high education exposure and dementia risk. The heterogeneity among studies was confirmed with a significance level of P<0.10 using the I2 statistic.
After reviewing titles, abstracts and full text, they found 91 studies exploring a prospective association between dementia and educational level. A total of 24 studies were eligible for inclusion in the qualitative synthesis, and 16 (11 for low education and 5 for high education) of them were eligible for the quantitative meta-analysis.
- Both low and high risk education showed a trend of dose-response relation with risk of dementia and Alzheimer’s disease (AD)
- For low education the pooled results showed a more significant increment of dementia or AD risk for high than low dose exposure
- For dementia risk
- Low exposure to education reduced the risk by 41% (RR, 0.59; 95% CI, 0.41 to 0.87; I2=77.4%; p=0.000)
- High exposure to education reduced the risk by 56% (RR, 0.44; 95% CI, 0.32 to 0.60; I2=41.5%; p=0.081)
- For AD risk
- Low exposure to education was reduced by 33% (RR, 0.67; 95% CI, 0.49 to 0.92; I2=37.5%; p=0.187)
- High exposure to education was reduced by 59% (RR, 0.41; 95% CI, 0.24 to 0.64; I2=30.6%; p=0.228)
- An inverse relation was identified between high education and dementia risk in the quantitative analysis and a decrease for dementia risk by 7% for per year increase in education
- Also, pooled results from studies which reported associations with per schooling year increase, revealed a mildly higher protection.
- For exposure level to low education, the risk for dementia was mildly elevated for per year decrease in education, but the results were not statistically significant.
The results of this meta-analysis are in concordance with those presented in the World Alzheimer Report, which state that education is an important modifiable factor for dementia. This paper states that high levels of education significantly reduce risk of dementia in a linear dose-response manner, identifying a linear trend between the two variables.
The main reason why education might influence dementia risk is that a lack of educational attainment is also associated with other risk factors for dementia such as lifestyle, cardiovascular risk, socioeconomic status and others. More than that though, educational attainment is positively associated with a healthier brain.
Strengths and limitations
This study did more than confirm the important role of education in lowering the risk of dementia. The authors also quantified the dose-response relationship between educational attainment and dementia or Alzheimer’s Disease.
The authors suggest a limitation of their work was that they restricted their literature search to articles written in English and those only available in the specific databases they searched. I want to state that a comparison of different education systems would have been very welcome, taking in consideration that although a great part of the studies came from Western populations, there were some from Asian populations also. And even in Western populations there are so many differences in educational systems across countries. They chose to exclude studies involving parental education and educational quality, but these are important factors that might contribute to higher or lower levels of risk among different societies.
This paper presents important modifiable factors for reducing the risk of dementia. Many people consider that everyone gets dementia if they live long enough, but this is not true. Dementia is not a normal part of the ageing process and the more we know about the risk factors of the disease, the more we can do to help prevent it from occurring.
Xu W, Tan L, Wang HF, Tan MS, Tan L, Li JQ, Zhao QF, Yu JT. (2015) Education and Risk of Dementia: Dose-Response Meta-Analysis of Prospective Cohort Studies. Molecular Neurobiology. 2015 May 17. [PubMed abstract]
Prince M. et al (2015) World Alzheimer Report 2015: The Global Impact of Dementia – An analysis of prevalence, incidence, cost and trends. Alzheimer’s Disease International. 2015.