Alzheimer’s Disease (AD) is the most common form of dementia which affects almost half a million people in the UK. The term ‘dementia’ describes a set of symptoms which can include loss of memory, mood changes, and problems with communication and reasoning. Alzheimer’s is a progressive disease, which means that gradually, over time, more parts of the brain are damaged. As this happens, the symptoms become more severe (1).
Despite the extensive use of drugs to treat the disease, the harsh reality is that we still have no cure that is genuinely effective. Therefore any progress in controlling AD will only be achieved by prevention, which means we need to focus on our understanding of the causes. According to a study led by Deborah Barnes, a mental health researcher at the San Francisco VA Medical Center, over half of all Alzheimer’s disease cases could potentially be prevented through lifestyle changes and treatment or prevention of chronic medical conditions. As a result of analyzing data from studies around the world involving hundreds of thousands of participants, she concluded that the biggest most significant risk factors for AD are, in descending order of magnitude, low education, smoking, physical inactivity, depression, mid-life hypertension, diabetes and mid-life obesity. Together, these risk factors are associated with up to 51 percent of AD cases worldwide (17.2 million cases) and up to 54 percent of those in the US (2.9 million cases) (2).
In this blog I will attempt to identify some of the dietary factors which are relevant. A recent study conducted at the Mayo Clinic found that people aged 70 and older who eat food high in carbohydrates have nearly four times the risk of developing mild cognitive impairment. Similar results were also obtained for those who consumed a diet which was high in sugar. By contrast, those who consumed diets with a high proportion of fat and protein relative to that of carbohydrates were less likely to develop the condition.
Researchers followed 1,230 people ages 70 to 89 who provided information on what they ate during the previous year. At that time, their cognitive function was evaluated by an expert panel of physicians, nurses and neuropsychologists. Of those participants, only the roughly 940 who showed no signs of cognitive impairment were asked to return for follow-up evaluations. About four years into the study, 200 of those 940 were beginning to show mild cognitive impairment, problems with memory, language, thinking and judgment that are greater than normal age-related changes.
Those who reported the highest carbohydrate intake at the beginning of the study were 1.9 times likelier to develop mild cognitive impairment than those with the lowest intake of carbohydrates. Participants with the highest sugar intake were 1.5 times likelier to experience mild cognitive impairment than those with the lowest levels.
But those whose diets were highest in fat — compared to the lowest — were 42 percent less likely to face cognitive impairment, and those who had the highest intake of protein had a reduced risk of 21 percent.
When total fat and protein intake were taken into account, people with the highest carbohydrate intake were 3.6 times likelier to develop mild cognitive impairment.
A study conducted in Rotterdam has found that those with diabetes were over 3 times as likely to develop dementia as those without. Patients being treated with insulin were at greater risk of dementia by a factor of 4(4).
Those with undiagnosed diabetes were more than 3 times as likely to develop AD compared with those free of diabetes(5).
The differences in the incidence of disease in diabetics is probably even greater than indicated in the various studies because those classed as “non-diabetics” invariably include diabetics which have not been diagnosed. This means that the values for those considered free of diabetes would be higher than those who are genuinely free of the disease.
These findings were effectively confirmed in a recent study conducted in the US (6). Over 2000 participants were monitored for blood glucose levels at least 5 times during the 5 years prior to the initiation of the investigation. Participants were assessed for dementia every 2 years. Diagnoses of dementia and of probable or possible AD were made on the basis of research criteria. At the outset, over 10% of the participants were diagnosed with diabetes. Over a median follow-up period of 6.8 years, dementia developed in 524 of the 2067 participants (25.4%), including 450 of the 1724 participants who did not have diabetes at the end of follow-up (26.1%) and 74 of the 343 participants who had diabetes at the end of follow-up (21.6%). What was especially interesting was that the incidence of dementia increased with the level of blood glucose for those without diabetes as well as for those with diabetes (6).
It is accepted that the level of blood glucose is determined by the presence in the diet of foods which break down rapidly to release fructose and glucose. Essentially these are sugar and refined carbohydrates, although it must be recognised that many of the so-called “complex carbohydrates” also make a contribution to the glucose in the blood. The importance of these findings is that even if diabetes has not been diagnosed it may well be possible to reduce the risks of developing AD by taking steps to lower the blood glucose.
According to Dr David Perlmutter, author of ”Grain Brain”. a person consuming a diet low carbohydrates and relatively high in fat has developed the ability to utilise fat as a source of energy (7). This means that glucose is not required to provide the energy and the blood glucose levels will remain quite low. As a consequence, the risks of developing AD, diabetes and various related diseases and conditions will also be lowered.
Unfortunately these usual advice given to patients with raised blood glucose is to REDUCE FAT and INCREASE CARBOHYDRATES, which has the effect of raising the blood glucose and therefore making things worse.
As will be clear to readers of my other contributions, there is now overwhelming evidence that a diet which is high in fat (except the trans fats and the omega-6s) is beneficial to health. At the same time it is crucial to limit the intake of all carbohydrates. By adopting this approach, the risks of developing heart disease, obesity and various cancers will be reduced. AD can now be added to this list.
- A Ott et al (1996) Diabetologia 39 (11) pp 1392-1397
- W L Xu (2009) Diabetologia 52 (6) pp 1031-1039