An impaired insulin response and poor glucose tolerance, two characteristics of diabetes, may lead to an increased risk of dementia and Alzheimer’s disease in later life according to a recent study published online in the journal Neurology on April 9.
The study, conducted by Swedish researchers, involved data from the Uppsala Longitudinal Study of Adult Men which followed 2,269 men aged 50 years in 1970 for an average period of 32 years. At the beginning of the study, the men were tested for both insulin response and glucose tolerance. At the conclusion of the study, 102 (4.5%) of the men had developed Alzheimer’s disease, 57 (2.5%) had developed vascular dementia, and 235 (10.4%) had been diagnosed with other forms of dementia.
The researchers found that those men with a poor response to insulin were much more likely to develop Alzheimer’s disease than those with a normal insulin response. Those in the bottom quarter for insulin response were almost twice as likely to develop Alzheimer’s disease as those in the top 25% for insulin response.
While impaired glucose tolerance was not associated with Alzheimer’s disease, it was associated with another form of dementia known as vascular dementia. Those in the bottom 25% in terms of glucose tolerance were around 2.2 times more likely to develop vascular dementia than those in the top 25%.
Vascular dementia is the second most common form of dementia behind Alzheimer’s disease. It occurs when blood flow to the brain is impaired causing brain cells to die due to a lack of oxygen.
The relationship between Alzheimer’s disease and poor insulin response was strongest in those who did not have a specific form of a gene called ApoE-4 which is associated with Alzheimer’s disease. Around 30% of the population is though to have at least one copy of ApoE-4.
According to lead researcher Elina Ronnemaa of the Uppsala University in Sweden: “Our results have important public health implications given the increasing numbers of people developing diabetes and the need for more powerful interventions.” Ronnemma added that insulin problems are an important risk factor for Alzheimer’s disease, particularly amongst those who do not have the high risk form of the ApoE gene.
Similar findings have been reported in earlier studies. In one study, published in 1996, Dutch researchers found that diabetics who required insulin were 3.2 times more likely to develop dementia than non-diabetics. That study found that the relationship was strongest with vascular dementia but was also observed in Alzheimer’s disease.
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