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Statistics for Business and Economics: Excel/Minitab Enhanced
Heinz Kohler
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Statistics in the News: Chapter 17 Multiple Regression and Correlation

Assessing the Link Between Diet and Dementia in the Elderly

Medical researchers seek to learn all they can about the causes of diseases and how these causes might respond to various forms of intervention. One recent study sought to shed light on the hypothesis that elevated plasma homocysteine levels may be associated with poor cognition and various forms of dementia among the elderly. Thus, a reduction in these levels might prevent those undesirable results.

The study followed the lives of 1,092 subjects, aged 68-97, who were initially free of dementia. After a median period of 8 years, some 111 of these individuals were diagnosed with dementia (83 of these with Alzheimer's disease). Consider the researchers' thoughts:

In the past, high plasma homocysteine levels, which rise in people whose diets are heavy with animal protein, have been shown to damage blood vessels and nerves. They have also been linked to strokes and heart attacks. Accordingly, the researchers suspected that low plasma homocysteine levels (which can be achieved by a diet favoring fruits and leafy vegetables containing plenty of folic acid and vitamins B6 and B12), might be associated with less damage to blood vessels and nerves and, thus, a lower incidence of dementia.

A multiple regression model related the appearance of dementia to a number of possible factors, including age, plasma levels of folate and vitamins B6 and B12, educational status, history of stroke, smoking status, alcohol intake, presence of diabetes, body mass, blood pressure, and more.

The results: High plasma homocysteine levels raised the risk of any type of dementia by 40 percent. They raised the risk of Alzheimer's disease by 80 percent. (95% confidence intervals for the associated relative risk ratios of 1.4 and 1.8 reached from 1.1 to 1.9 in the former case and from 1.3 to 2.5 in the latter case.) Interestingly, people whose homocysteine levels initially exceeded 14 micromoles per liter of blood, one quarter of the group, were found to have nearly twice the risk of getting Alzheimer's as others with much lower levels. The researchers concluded that the risk of dementia could probably be reduced substantially by adding large doses of folate and vitamins B6 and B12 to the diets of most people.

Caution: It is not clear that high plasma homocysteine levels that precede the onset of dementia also cause it. It is also possible that a third factor is at work, simultaneously causing high levels of plasma homocysteine and dementia.

Sources: Sources: Adapted from Joseph Loscalzo, "Homocysteine and Dementias," The New England Journal of Medicine, February 14, 2002, pp. 466-468; Sudha Seshadri et al., "Plasma Homocysteine as a Risk Factor for Dementia and Alzheimer's Disease," ibid., pp. 476-483; and Denise Grady, "Alzheimer's May Be Linked to Normal Diet Byproduct," The New York Times, February 14, 2002, p. A25.