Oxidative stress isn’t the only reason why your diet can affect your risk of developing Azlheimer’s. Both diet and lack of exercise are also contributing factors for insulin resistance. Insulin resistance is where the cells of the body respond less to the effects of insulin and therefore glucose uptake is reduced. It can lead to conditions such as hypertension, diabetes and cardiovascular disease; all of which increase the risk of Alzheimer’s. It is estimated that 25-30% of people over the age of 65 have insulin resistance.
What is Insulin?
Insulin is necessary for brain cell function. It facilitates the uptake of glucose by the cells for use in respiration which creates the cell’s energy. The effects of insulin on Alzheimer’s have been investigated using a pilot study into intranasal insulin treatment. Insulin was administered to Alzheimer’s patients daily from a device which sprayed the hormone directly into the nasal passages. Over the four year period, the patients’ cognitive abilities were assessed. Interestingly, recall was improved further in patients receiving a lower dose of insulin but not so in those receiving a higher dose. The researchers emphasise that this was a very small study of only 104 subjects, and so more extensive studies will need to be carried out to understand these effects.

Interesting Links...
Link to diabetes
  Insulin resistance is perhaps mainly associated with diabetes. Sufferers of diabetes have abnormally high blood sugar levels due to either an underproduction of insulin or a resistance of their body cells to the effects of insulin. They are also much more likely to develop Alzheimer’s disease. This provides further evidence from the previously mentioned APL-1 gene that diabetes and Alzheimer’s are linked.
Link to cardiovascular disease
Insulin resistance is also a risk factor for cardiovascular disease, which is one of the main environmental risk factors for Alzheimer’s. Cardiovascular disease affects the blood supply to the brain. If this blood supply is inefficient, there will be a lack of oxygen for the brain cells to carry out respiration.
Link to cholesterol levels
As previously mentioned, high levels of cholesterol are essential for the formation of amyloid plaques, as cholesterol facilitates the release of amyloid beta fragments from the c99 protein. But cholesterol can also contribute to the development of Alzheimer’s disease by its role in causing hypertension. High levels of cholesterol can lead to deposits forming in the arteries called atheromas. These narrow the lumen of the arteries and increase blood pressure. Hypertension is a risk factor for cardiovascular disease, and is also a known risk factor of Alzheimer’s disease. Statins are drugs that control cholesterol levels and are prescribed for the prevention of heart disease. Interestingly, recent experiments into mice found that use of the statins actually improved learning and memory function in mice. More research is needed before we could know if statins can be prescribed for Alzheimer’s, but this study does show evidence for the relationship between heart disease and Alzheimer’s.

The effects of Alcohol and Smoking
Other lifestyle choices are known to affect Alzheimer’s. One advised preventative measure of Alzheimer’s is to consume alcohol in moderation. Excessive alcohol consumption is known to lead to hypertension and insulin resistance. However alcohol also contains antioxidants, so it can be beneficial to drink it in controlled amounts. Smoking is also thought to contribute to Alzheimer’s disease. Although early studies suggested that smoking decreases the risk of Alzheimer’s, this has been widely discredited. Eleven of the controversial studies were found to have been conducted by researchers with connections to the tobacco industry. More current and reliable studies suggest that heavy smoking can increase a person’s susceptibility to Alzheimer’s, and that passive smoking may also have an effect.
Alzheimer’s Association, 2012. Inside the Brain: An interactive tour [online] Available at: <https://www.alz.org/braintour/alzheimers_changes.asp> [Accessed 18 July 2012]

Alzheimer’s Society, 2010. Am I at risk of developing dementia? [online] Available at <http://www.alzheimers.org.uk/site/scripts/documents_info.php?documentID=102> [Accessed 18 July 2012]

Craft, S. et al, 2012. Intranasal Insulin Therapy for Alzheimer Disease and Amnestic Mild Cognitive Impairment; A Pilot Clinical Trial. Archives of Neurology [online] Volume 69, Number 1. Available at <http://archneur.jamanetwork.com/article.aspx?articleid=1107947> [Accessed 18 July 2012]

Goldacre, B. 2010.Smoking prevents Alzheimer’s? It depends who you ask. The Guardian [online] Available at: <http://www.guardian.co.uk/science/2010/mar/05/smoking-alzheimers-goldacre-bad-science> [Accessed 18 July 2012]

HBO : Documentaries : The Alzheimer’s Project, 2012. The Connection between Insulin and Alzheimer’s [online video] Available at: <http://www.hbo.com/alzheimers/supplementary-the-connection-between-insulin-and-alzheimers.html> [Accessed 12 July 2012]

Holehouse, M., 2012. Statins could stave off symptoms of Alzheimer's, study finds, The Telegraph [online] Available at: < http://www.telegraph.co.uk/health/elderhealth/9184705/Statins-could-stave-off-symptoms-of-Alzheimers-study-finds.html> [Accessed 15 September 2012]

Orsitto, G. et al. 2012. Relation of Secondhand Smoking to Mild Cognitive Impairment in Older Inpatients Scientific World Journal [online] Available at: <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3361321/> [Accessed July 18 2012]