High cholesterol levels in middle age do not appear to increase women's risk of developing Alzheimer's disease and other forms of dementia later in life, new Johns Hopkins-led research finds, despite a body of scientific evidence long suggesting a link between the two.
What the study, published online in the journal Neurology, does find is that women whose cholesterol levels decline from middle age to old age are at 2.5 times greater risk of developing the memory-wasting diseases than those whose cholesterol stayed the same or increased over the years.
"Our research refutes the notion that high cholesterol in midlife is a risk factor for Alzheimer's disease, at least among women," says Michelle M. Mielke, Ph.D., an assistant professor of psychiatry at the Johns Hopkins University School of Medicine and the study's lead author.
Even though Mielke and her colleagues found no link between high middle-age cholesterol levels and dementia risk, Mielke cautions that people still need to watch their cholesterol. High cholesterol levels are linked to cardiovascular and other diseases. Cholesterol levels can be kept in check through diet, exercise and medication.
Mielke and her colleagues examined data from the Prospective Population Study of Women, which began in 1968 and consisted of 1,462 Swedish women ages 38 to 60. Follow-ups were conducted at four intervals across the intervening decades, with the most recent examinations concluding in 2001. As part of the study, the women were given physical exams, heart tests, chest x-rays and blood tests. The group was also surveyed for smoking habits, alcohol and medication use, education and medical history. Throughout the study, body mass index (BMI), a measurement of weight-per-height, and blood pressure were taken. Women were assessed for dementia throughout the 32 years of follow-up between 1968 and 2001. In 2001, 161 of the original group had been diagnosed with Alzheimer's or other forms of dementia, but the youngest group was just reaching age 70.
Despite the advances being made in biomarker and other dementia research, the biggest known risk factor for these neurodegenerative diseases is old age.
Mielke says that later in life, women with slightly higher body mass index, higher levels of cholesterol and higher blood pressure tend to be healthier overall than those whose weight, cholesterol and blood pressure are too low. But it is unclear whether "too low" cholesterol, BMI and blood pressure are risk factors for dementia or if they could be signs that dementia is developing, she says. For example, an inadvertent loss of weight often precedes the development of dementia, she says, but the exact cause is unclear.
The study was supported by the National Institute of Health, the National Institute on Aging, the National Institutes of Neurological Disorders and Stroke, the Swedish Research Council, the Swedish Brain Power Project, the University of Gothenburg, Swedish Council for Working Life and Social Research, Swedish Alzheimer Association, European Commission Seventh Framework Program, Svenssons Foundation, the Swedish Society of Medicine, the Söderström-Königska Nursing Home Foundation, the Foundation för Gamla Tjänarinnor, Hjalmar Svenssons Foundation, the Swedish Society of Medicine, the Göteborg Medical Society, the Lions Foundation, the Dr. Felix Neubergh Foundation, the Wilhelm and Martina Lundgren Foundation, the Elsa and Eivind Kison Sylvan Foundation, and the Alzheimer's Association Zenith Award.
Johns Hopkins associate professor Peter P. Zandi, Ph.D., also participated in the study as well as researchers from SUNY-Downstate Medical Center in Brooklyn, N.Y., and the University of Gothenburg in Sweden.