A new long-term study suggests that cholesterol levels in middle-aged women may not be linked to the later development of Alzheimer's disease and other forms of dementia, despite a body of prior evidence suggesting such a link. However, the new study shows that large decreases in cholesterol levels in old age could be a better predictor of developing Alzheimer's disease. Researchers reported these findings in the November 10 online issue of Neurology.
Michelle M. Mielke, PhD, Assistant Professor, Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, and colleagues examined data from the Prospective Population Study of Women, which began in 1968 and consisted of 1,462 dementia-free Swedish women between the ages of 38 and 60. Follow-ups were conducted at four intervals across the intervening decades, with the final examination occurring in 2001. The women received a physical examination, heart tests, chest x-rays, and blood tests. The women were also surveyed for smoking habits, alcohol and medication use, education, and medical history. Throughout the study, body mass index (BMI) and blood pressure were monitored. At four points the women were assessed for dementia.
After 32 years, 161 women had developed dementia. The researchers found that cholesterol measured in middle or old age showed no correlation to dementia. This, they reported, conflicts with previously reported findings. The research team also found that the women whose cholesterol levels decreased the most from middle to older age were more than twice as likely to develop dementia as those whose cholesterol levels increased or remained constant. The risk of Alzheimer's disease increased from 8.9% for those who maintained or increased cholesterol over the course of the study to 17.5% for women with the greatest decline in cholesterol.
Cholesterol Recommendation
Dr. Mielke and colleagues said that decreased cholesterol levels greater than what would be expected in old age may be a more accurate indicator of dementia risk than cholesterol levels in middle age. In later life, women with slightly higher BMI, higher levels of cholesterol, and higher blood pressure tend to be healthier overall than those whose weight, cholesterol, and blood pressure are too low, the researchers pointed out. It is unclear, they said, whether "too low" cholesterol, BMI, and blood pressure are risk factors for dementia or if they could be signs that dementia is developing.
Even though the researchers found no link between midlife cholesterol levels and dementia risk, they nevertheless recommend that people should still follow heart-healthy guidelines. "Cholesterol should still be monitored and treated through diet, exercise, and medication for cardiovascular and overall health."
Impetus for Change?
Addressing the clinical practice implications of the present findings in an accompanying editorial, Mary N. Haan, MPH, DrPH, from the University of California, San Francisco, commented that "because midlife vascular risk factors are already well-recognized targets for prevention of cardiovascular disease, adding risk reduction for dementia is something like gilding the lily."
However, she said, based on the current evidence we cannot tell middle-aged patients that lowering midlife cholesterol level, or tell older patients that maintaining cholesterol level will necessarily reduce their risk of dementia. "Because early-midlife and late-life factors apparently differ in their effects on late-life dementia, different preventive strategies should be investigated. Effective primary prevention of dementia may need to address early and midlife risk factors, while, in late life, 'prevention' may necessarily focus on delaying progression of pathology and symptoms, with targeted risk factors dependent on the stage of life."