On 2015 Feb 15, William Grant commented:

The effect of diet on risk of Alzheimer's disease is very strong; vitamin D also reduces risk

The paper by Deckers and colleagues used the Delphi consensus approach to rank the target risk factors for dementia [1]. Diet was ranked 6th out of 11 factors in the Delphi ranking round 2, behind depression, diabetes, cognitive ability, physical activity, and midlife hypertension.

Ref. 1 relied primarily on prospective observational studies. While such studies are valuable, they are not the only way to assess risk. Another way is through ecological studies, either geographical or temporal. The first study to identify diet as an important risk factor for Alzheimer's disease was a multi-country ecological study [2]. It was discussed in two subsequent papers [3,4]. The most dramatic application of the ecological approach to studying the effect of diet on risk of Alzheimer's disease was in analyzing trends of Alzheimer's disease rates in Japan. The increase in Alzheimer's disease rates for elderly people in Japan from 1% in 1985 to 7% in 2008 was attributed to the nutrition transition from the traditional Japanese diet to the Western diet [5]. In addition, dietary advanced glycation end products from food cooked at high temperatures or aged as in hard cheese have been identified as an important risk factor for Alzheimer's disease [6, 7]. Diet is also a well known risk factor for diabetes.

A factor not mentioned but one that is gaining acceptance is low 25-hydroxyvitamin D [25(OH)D] concentrations [8]. Low 25(OH)D concentrations have been reported as a risk factor for Alzheimer's disease and dementia [9], diabetes mellitus [10], and cognitive dysfunction [11].

References 1. Deckers K, van Boxtel MP, Schiepers OJ, de Vugt M, Muñoz Sánchez JL, Anstey KJ, Brayne C, Dartigues JF, Engedal K, Kivipelto M, Ritchie K, Starr JM, Yaffe K, Irving K, Verhey FR, Köhler S. Target risk factors for dementia prevention: a systematic review and Delphi consensus study on the evidence from observational studies. Int J Geriatr Psychiatry. 2015;30(3):234-46. 2. Grant WB. Dietary links to Alzheimer's disease. Alz Dis Rev. 1997;2:42-55. http://www.sunarc.org/JAD97.pdf) 3. Grant WB. Dietary links to Alzheimer’s disease: 1999 update. J Alz Dis. 1999;1197-201. 4. Grant WB, Campbell A, Itzhaki RF, Savory J, The significance of environmental factors in the etiology of Alzheimer’s disease. J Alz Dis. 2002;4:179-89. 5. Grant WB. Trends in diet and Alzheimer’s disease during the nutrition transition in Japan and developing countries. J Alzheimers Dis. 2014;38(3):611-20. 6. Cai W, Uribarri J, Zhu L, Chen X, Swamy S, Zhao Z, Grosjean F, Simonaro C, Kuchel GA, Schnaider-Beeri M, Woodward M, Striker GE, Vlassara H. Oral glycotoxins are a modifiable cause of dementia and the metabolic syndrome in mice and humans. Proc Natl Acad Sci U S A. 2014;111:4940-5. 7. Perrone L, Grant WB. Observational and ecological studies of dietary advanced glycation end products in national diets and Alzheimer’s disease incidence and prevalence. J Alzheimers Dis. 2015 Jan 29. [Epub ahead of print] 8. Grant WB. Does vitamin D reduce the risk of dementia? J Alzheimers Dis. 2009;17(1):151-9. 9. Littlejohns TJ, Henley WE, Lang IA, Annweiler C, Beauchet O, Chaves PH, Fried L, Kestenbaum BR, Kuller LH, Langa KM, Lopez OL, Kos K, Soni M, Llewellyn DJ. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. 2014;83(10):920-8. 10. Song Y, Wang L, Pittas AG, Del Gobbo LC, Zhang C, Manson JE, Hu FB. Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2013;36(5):1422-8. 11. Annweiler C, Dursun E, Féron F, Gezen-Ak D, Kalueff AV, Littlejohns T, Llewellyn DJ, Millet P, Scott T, Tucker KL, Yilmazer S, Beauchet O. 'Vitamin D and cognition in older adults': updated international recommendations. J Intern Med. 2015;277(1):45-57.

On 2015 Feb 15, William Grant commented:

The effect of diet on risk of Alzheimer's disease is very strong; vitamin D also reduces risk

The paper by Deckers and colleagues used the Delphi consensus approach to rank the target risk factors for dementia [1]. Diet was ranked 6th out of 11 factors in the Delphi ranking round 2, behind depression, diabetes, cognitive ability, physical activity, and midlife hypertension.

Ref. 1 relied primarily on prospective observational studies. While such studies are valuable, they are not the only way to assess risk. Another way is through ecological studies, either geographical or temporal. The first study to identify diet as an important risk factor for Alzheimer's disease was a multi-country ecological study [2]. It was discussed in two subsequent papers [3,4]. The most dramatic application of the ecological approach to studying the effect of diet on risk of Alzheimer's disease was in analyzing trends of Alzheimer's disease rates in Japan. The increase in Alzheimer's disease rates for elderly people in Japan from 1% in 1985 to 7% in 2008 was attributed to the nutrition transition from the traditional Japanese diet to the Western diet [5]. In addition, dietary advanced glycation end products from food cooked at high temperatures or aged as in hard cheese have been identified as an important risk factor for Alzheimer's disease [6, 7]. Diet is also a well known risk factor for diabetes.

A factor not mentioned but one that is gaining acceptance is low 25-hydroxyvitamin D [25(OH)D] concentrations [8]. Low 25(OH)D concentrations have been reported as a risk factor for Alzheimer's disease and dementia [9], diabetes mellitus [10], and cognitive dysfunction [11].

References 1. Deckers K, van Boxtel MP, Schiepers OJ, de Vugt M, Muñoz Sánchez JL, Anstey KJ, Brayne C, Dartigues JF, Engedal K, Kivipelto M, Ritchie K, Starr JM, Yaffe K, Irving K, Verhey FR, Köhler S. Target risk factors for dementia prevention: a systematic review and Delphi consensus study on the evidence from observational studies. Int J Geriatr Psychiatry. 2015;30(3):234-46. 2. Grant WB. Dietary links to Alzheimer's disease. Alz Dis Rev. 1997;2:42-55. http://www.sunarc.org/JAD97.pdf) 3. Grant WB. Dietary links to Alzheimer’s disease: 1999 update. J Alz Dis. 1999;1197-201. 4. Grant WB, Campbell A, Itzhaki RF, Savory J, The significance of environmental factors in the etiology of Alzheimer’s disease. J Alz Dis. 2002;4:179-89. 5. Grant WB. Trends in diet and Alzheimer’s disease during the nutrition transition in Japan and developing countries. J Alzheimers Dis. 2014;38(3):611-20. 6. Cai W, Uribarri J, Zhu L, Chen X, Swamy S, Zhao Z, Grosjean F, Simonaro C, Kuchel GA, Schnaider-Beeri M, Woodward M, Striker GE, Vlassara H. Oral glycotoxins are a modifiable cause of dementia and the metabolic syndrome in mice and humans. Proc Natl Acad Sci U S A. 2014;111:4940-5. 7. Perrone L, Grant WB. Observational and ecological studies of dietary advanced glycation end products in national diets and Alzheimer’s disease incidence and prevalence. J Alzheimers Dis. 2015 Jan 29. [Epub ahead of print] 8. Grant WB. Does vitamin D reduce the risk of dementia? J Alzheimers Dis. 2009;17(1):151-9. 9. Littlejohns TJ, Henley WE, Lang IA, Annweiler C, Beauchet O, Chaves PH, Fried L, Kestenbaum BR, Kuller LH, Langa KM, Lopez OL, Kos K, Soni M, Llewellyn DJ. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. 2014;83(10):920-8. 10. Song Y, Wang L, Pittas AG, Del Gobbo LC, Zhang C, Manson JE, Hu FB. Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2013;36(5):1422-8. 11. Annweiler C, Dursun E, Féron F, Gezen-Ak D, Kalueff AV, Littlejohns T, Llewellyn DJ, Millet P, Scott T, Tucker KL, Yilmazer S, Beauchet O. 'Vitamin D and cognition in older adults': updated international recommendations. J Intern Med. 2015;277(1):45-57.