There is evidence from epidemiological studies that dietary and lifestyle factors may reduce the risk of dementia [i]. Studies of centenarians in the Japanese prefecture of Okinawa, for example, have indicated that they have dementia rates 30 to 40 per cent lower than similarly aged Americans.
Research at Oxford University and elsewhere has provided clear evidence that Alzheimers is not an inevitable part of ageing but is a disease [ii]. There is also evidence of a correlation between coronary heart disease, homocysteine level and risk of dementia [iii, iv].
It is well-established from numerous long-term health studies that energy-dense diets high in saturated fat, sugar and salt, and low in fruit, vegetables, fibre and essential fatty acids increase the risk of developing heart disease (World Health Report 2002). There is therefore significant interest in whether such diets may also increase the risk of developing dementia and whether homocysteine level is a modifiable risk factor.
The potential role of folate and vitamin B12 in reducing homocysteine levels has been investigated by the University of Oxford Project to Investigate Memory and Ageing – OPTIMA – by the US National Institute on Aging and by the Alzheimer’s Disease Co-operative Study. Recent results suggest that high doses of B vitamins do not slow cognitive decline in people with Alzheimer’s disease (see Reuters news report, October 2008). The study did not look at whether lowering homocysteine much earlier in life would prevent or delay Alzheimer’s.
The problem with this type of clinical trial is that the effects of a small number of nutrients are examined in isolation, often at much higher doses than would be typical in a normal diet. In real life, the protective effects of a diet are likely to occur due to complex interactions between a large number of nutrients present in relatively small amounts.
Research published in the January 2009 edition of the journal Diabetes
shows that developing type 2 diabetes before the age of 65 corresponds to a 125 per cent increased risk for Alzheimer’s disease [v]. According to the authors, the results of the study implicate adult choices such as exercise, diet and smoking, as well as glycaemic control in patients with diabetes, in affecting risk for Alzheimer’s disease.
Until further research uncovers the precise risk factors for development of dementia, we may be well-advised to follow the dietary principles of the Okinawan elders:
- Cut excess calories – eat more high fibre, unrefined foods which are high in nutrients but low in calories
- Eat mostly complex carbohydrates – more whole grains, pulses, vegetables, fruit, nuts, seeds and less refined sugar and refined white flour products
- Eat less animal protein and more plant protein – less red meat and more fish, and more soy products
- Eat more good (unsaturated) fats and less bad (saturated) fats – more oily fish, less animal fat and more plant fats
Learn about how to cook and eat healthy food based on the dietary principles of the Okinawan elders at Cooking for Health classes held throughout the year in Somerset, UK.
[i] Yamada, M. et al. J. Am. Geriatr. Soc, 1999, 47: 189-195; Kokmen, E. et al., Mayo Clin Proc 1996, 71: 275-282; Ogura, C. et al. International J. Epidemiol., 1995, 24: 373-380.
[ii] Jobst KA, Smith AD, Szatmari M, Esiri MM, Jaskowski A, Hindley N, McDonald B, Molyneux AJ. Rapidly progressing atrophy of medial temporal lobe in Alzheimer’s disease. Lancet. 1994;343:829-30
[iii] Clarke R, Smith AD, Jobst KA, Refsum H, Sutton L, Ueland PM. Folate, vitamin B12, and serum total homocysteine levels in confirmed Alzheimer disease. Arch Neurol. 1998;55:1449-55; Smith AD. Homocysteine, B vitamins, and cognitive deficit in the elderly. Am J Clin Nutr. 2002;75:785-6.
[iv] Sudha Seshadri, M.D. et al. Plasma Homocysteine as a Risk Factor for Dementia and Alzheimer’s Disease. New England Journal of Medicine, Volume 346:476-483, 2002.
[v] Weili Xu et al. “Mid- and Late-Life Diabetes in Relation to the Risk of Dementia. Diabetes, January 2009.