A Harvard epidemiologist offered some good news amid the doom and gloom that generally surrounds discussions of Alzheimer’s disease. Its incidence — the number of people diagnosed annually — has fallen substantially in recent years.
Albert Hofman, chair of the Harvard T.H. Chan School of Public Health’s epidemiology department, said that several studies have confirmed a 20 percent decline in incidence from 1990 to 2010, measured decade over decade. That positive is masked by a continuing rise in the overall number of cases, due to the fact that people continue to live longer and so the number of elderly continues to rise.
Much recent Alzheimer’s research has focused on genetic factors — some 30 genes have been implicated so far — but Hofman said those genes have been shown to account for less than a quarter of the cases. Further, he said that if the disease had largely genetic origins, the observed decline in incidence would be even more mysterious, since human genes don’t change quickly enough to account for the drop seen over just two decades.
Hofman, who has led large-cohort studies including the Alzheimer Cohorts Consortium and the Rotterdam Study, said he believes that most Alzheimer’s cases are due to non-genetic factors, which include trauma, such as concussions; endocrine factors relating to hormones; inflammatory factors; and vascular factors, relating to blood flow and blood vessel health.
Of these, Hofman said vascular factors appear to be most important. He described a scenario where poor blood vessel health and the buildup of deposits in the arteries over many years constrict blood flow to the brain. Ultimately, he said, that kills nerve cells and sparks the body’s response, resulting in the plaques and tangles that characterize Alzheimer’s.
If that’s the case, he said, the decline in incidence is easier to explain. Changes in lifestyle, reduced smoking, and the use of new medicines like statins to fight heart attack, diabetes, stroke, and high blood pressure are likely also improving brain health. That would also mean, he said, that continued improvement in lifestyles — eating healthier and exercising regularly throughout life — will continue to bring down Alzheimer’s rates.
Hofman, the Stephen B. Kay Family Professor of Public Health and Clinical Epidemiology at the Harvard Chan School, spoke Monday evening at the Radcliffe Institute for Advanced Study’s Knafel Center. His talk, “The Alzheimer Enigma: The Causes of the Dementia Epidemic,” was part of the institute’s epidemics science lecture series and was introduced by Janet Rich-Edwards, co-director of the Radcliffe Institute’s Science Program and associate professor of epidemiology at the Harvard Chan School and of medicine at Harvard Medical School.