Derby CA, Katz MJ, Lipton RB, Hall CB.
Trends in Dementia Incidence in a Birth Cohort Analysis of the Einstein Aging Study.
JAMA Neurol. 2017 Sep 5;
PubMed.
This interesting paper agrees well with the findings in our NEJM paper (Satizabal et al., 2016) that the sharpest decline was in the last epoch. Also that decline in vascular risk factors does not "explain" the trend. And the increase in diabetes risk over time.
It extends our study by showing the same effect in a multiethnic, geographically distant cohort.
The birth cohort effect (persons born after 1929) is intriguing but will need replication in other cohorts. This important insight compels us to search for novel social and environmental factors that may have impacted this birth cohort before birth, in childhood or as young/middle-aged adults. Changes in nutrition, education, lead levels, other pollutants, infections all occurred and would be worth examining in cohorts and in animal models.
References:
Satizabal CL, Beiser AS, Chouraki V, Chêne G, Dufouil C, Seshadri S.
Incidence of Dementia over Three Decades in the Framingham Heart Study.
N Engl J Med. 2016 Feb 11;374(6):523-32.
PubMed.
This paper adds some important new evidence about the declining trend in the incidence of dementia in the United States. The data presented in Figure 1 suggest a few observations:
The decline in incidence within each age group considered has been continuing over several sequential decades of year of birth. There has been an acceleration for persons born in the middle or late 1920s; however, the decline was evident also for the cohorts before.
The decline in incidence was sizable.
The decline does not seem to be explained by trends in education, racial composition, or cardiovascular risk factors.
The study has some limitations:
The number of incident cases of dementia was small for more refined analyses.
The number became particularly small for the more recent birth cohorts.
It was impossible to conduct analyses separating Alzheimer’s disease from other types of dementia.
The incidence of dementia below the age of 70 years was not studied.
In a recent invited review, I emphasized the importance of considering year of birth and birth cohort effects in our efforts to explain the decline in the incidence of dementia (Rocca 2017). Combining the birth cohort analyses from our initial study in Rochester, Minnesota (Rocca et al., 2011) with the study conducted in western Pennsylvania (Dodge et al., 2014) and with the present study from New York, we get the impression that the decline in incidence is more evident for persons born after the late 1920s or early 1930s.
More studies are needed to explain the birth cohort effects observed. Derby and colleagues mention the possible effects of changes in diet. I think that changes in diet, especially for the mother during pregnancy, may be a crucial factor. I also noted that the persons born in 1929 were approximately of age 10–16 during World War II (1939–45), and the persons born thereafter were children during the war. It is possible that having lived most of their life in the post-war era protected these cohorts against dementia. In my invited review, I further discussed some of the social, cultural, political, technological, and medical events that took place after the World War II (Rocca 2017).
References:
Rocca WA.
Time, Sex, Gender, History, and Dementia.
Alzheimer Dis Assoc Disord. 2017 Jan-Mar;31(1):76-79.
PubMed.
Rocca WA, Petersen RC, Knopman DS, Hebert LE, Evans DA, Hall KS, Gao S, Unverzagt FW, Langa KM, Larson EB, White LR.
Trends in the incidence and prevalence of Alzheimer's disease, dementia, and cognitive impairment in the United States.
Alzheimers Dement. 2011 Jan;7(1):80-93.
PubMed.
Dodge HH, Zhu J, Lee CW, Chang CC, Ganguli M.
Cohort effects in age-associated cognitive trajectories.
J Gerontol A Biol Sci Med Sci. 2014 Jun;69(6):687-94. Epub 2013 Nov 23
PubMed.
Comments
Glenn Biggs Institute of Alzheimer's, UT Health
This interesting paper agrees well with the findings in our NEJM paper (Satizabal et al., 2016) that the sharpest decline was in the last epoch. Also that decline in vascular risk factors does not "explain" the trend. And the increase in diabetes risk over time.
It extends our study by showing the same effect in a multiethnic, geographically distant cohort.
The birth cohort effect (persons born after 1929) is intriguing but will need replication in other cohorts. This important insight compels us to search for novel social and environmental factors that may have impacted this birth cohort before birth, in childhood or as young/middle-aged adults. Changes in nutrition, education, lead levels, other pollutants, infections all occurred and would be worth examining in cohorts and in animal models.
References:
Satizabal CL, Beiser AS, Chouraki V, Chêne G, Dufouil C, Seshadri S. Incidence of Dementia over Three Decades in the Framingham Heart Study. N Engl J Med. 2016 Feb 11;374(6):523-32. PubMed.
View all comments by Sudha SeshadriMayo Clinic
This paper adds some important new evidence about the declining trend in the incidence of dementia in the United States. The data presented in Figure 1 suggest a few observations:
The study has some limitations:
In a recent invited review, I emphasized the importance of considering year of birth and birth cohort effects in our efforts to explain the decline in the incidence of dementia (Rocca 2017). Combining the birth cohort analyses from our initial study in Rochester, Minnesota (Rocca et al., 2011) with the study conducted in western Pennsylvania (Dodge et al., 2014) and with the present study from New York, we get the impression that the decline in incidence is more evident for persons born after the late 1920s or early 1930s.
More studies are needed to explain the birth cohort effects observed. Derby and colleagues mention the possible effects of changes in diet. I think that changes in diet, especially for the mother during pregnancy, may be a crucial factor. I also noted that the persons born in 1929 were approximately of age 10–16 during World War II (1939–45), and the persons born thereafter were children during the war. It is possible that having lived most of their life in the post-war era protected these cohorts against dementia. In my invited review, I further discussed some of the social, cultural, political, technological, and medical events that took place after the World War II (Rocca 2017).
References:
Rocca WA. Time, Sex, Gender, History, and Dementia. Alzheimer Dis Assoc Disord. 2017 Jan-Mar;31(1):76-79. PubMed.
Rocca WA, Petersen RC, Knopman DS, Hebert LE, Evans DA, Hall KS, Gao S, Unverzagt FW, Langa KM, Larson EB, White LR. Trends in the incidence and prevalence of Alzheimer's disease, dementia, and cognitive impairment in the United States. Alzheimers Dement. 2011 Jan;7(1):80-93. PubMed.
Dodge HH, Zhu J, Lee CW, Chang CC, Ganguli M. Cohort effects in age-associated cognitive trajectories. J Gerontol A Biol Sci Med Sci. 2014 Jun;69(6):687-94. Epub 2013 Nov 23 PubMed.
View all comments by Walter A. RoccaMake a Comment
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