Midlife vascular risk factors and their association with dementia deaths: results from a Norwegian prospective study followed up for 35 years.

There is growing evidence that midlife risk factors for vascular disease also are risk factors for dementia, but there is still need for long-term observational studies to address this. Our objective was to investigate the association of midlife vascular disease risk factors with dementia death. Participants were included in The Norwegian Counties Study (NCS) in the period 1974-78, aged 35-50 years at baseline. Information from NCS was linked with the Cause of Death Registry through the year 2009 using the unique personal identification number. The study included 48,793 participants, 1.5 million person years and 486 dementia deaths (187 Alzheimer's; 299 non-Alzheimer's dementia). Cox regression for cause-specific hazards was used. Dementia death was associated with increased total cholesterol levels (>7.80 vs. <5.20 mmol/l: HR=2.01, 95% confidence interval 1.37-2.93); diabetes (HR=2.43, 95% CI 1.40-4.32) and low body mass index (<20 kg/m(2) vs. 20-25 kg/m(2): HR=1.76, 95% CI 1.15-2.68) in midlife. The associations remained after adjustment for other vascular risk factors and educational level. Smoking status or blood pressure in midlife was not significantly associated with risk of dementia death, although the results indicate a possible increased risk in heavy smokers. People suffering from high cholesterol levels, diabetes or underweight in midlife are at increased risk of dying from or with dementia later in life. Our findings add to previous results suggesting that intervention in midlife may be important. To better understand the mechanisms involved in the associations between midlife underweight, diabetes, and elevated cholesterol level and late-life dementia death, these links need to be further investigated.