Early intervention is key when trying to combat dementia-related disease. A new long-term study by researchers at Michigan State University has provided evidence that a straightforward scratch-and-sniff test could effectively direct doctors towards those with a high risk of developing Parkinson's years before the disease exhibits notable symptoms.

Strong research from a variety of sources has previously suggested that a decrease in a person's sense of smell could be linked to the very early stages of Alzheimer's disease. This new study, conducted over 10 years, has focused on the development of Parkinson's disease in a multiracial cohort of subjects.

"One of the key differences in our study was we followed older white and black participants for an average of about 10 years, much longer than any other previous study," says lead author Honglei Chen.

The study followed 2,462 subjects split into two groups based on racial backgrounds (1,510 white and 952 black). Each subject was initially tested by smelling 12 common odors, ranging from cinnamon and lemon, to gasoline and soap. After labeling each participant with a sense of smell that was either poor, medium or good, their health was monitored for the following decade.

Forty-two people in the study went on to develop Parkinson's disease, with those found to have a poor sense of smell at the beginning of the study being five times more likely to be struck down with the disease. After adjusting for other mitigating factors that could affect one's sense of smell, such as smoking or head injury, the researchers noted that the results remained the same.

The study also found that trend was primarily only evident in white participants, with Professor Chen noting, "we found no statistical significance for a link between poor sense of smell and Parkinson's disease in blacks, but that may have been due to the small sample size and more research is needed."

The study is yet another piece of evidence in the growing body of proof suggesting a strong connection between the early onset of diseases such as Parkinson's and Alzheimer's, and the reduction of a person's sense of smell. However, the results of this study could indicate the correlation may be more complicated than previously considered with more research needed to understand how certain other characteristics, such as race, could affect the results.

"More research is needed before the smell test can be used as a screening tool for Parkinson's, but we are definitely on to something and our goal now is to better characterize populations that are at higher risk for the disease and to identify other factors involved," says Professor Chen.

The recent study was published in the journal Neurology.