Often when we think of scientific studies, we imagine a scientist conducting an experiment in which a variable is manipulated to determine the effect on a subject. A clinical trial is a great example. Patients with a specific illness are given an experimental drug. Their outcomes are compared to patients who aren’t given the drug. From these results, we can draw conclusions about whether or not the experimental drug is effective. This kind of study is also called an interventional study because the researchers have intervened in the natural progression of disease.
But this isn’t the only type of scientific study. Sometimes there are ethical or logistical reasons interventional studies are impossible. For example, we wouldn’t withhold a specific nutrient from a child in order to see if it stunts their growth. Another factor is the complexity of the problem we’re trying to understand. Conditions like heart disease and aging are multifactorial, meaning that many different factors interact to cause the phenomena we observe. This type of research question requires a different approach. Observational studies are often the answer. This kind of research design doesn’t involve manipulating a variable like diet or temperature. Instead, the researchers observe and measure various factors to learn how they are related to each other.
The Dog Aging Project is a longitudinal observational study. Typically, this means following the same research subjects over time (the longitudinal part of the study) and measuring, but not manipulating, the same variables over time (the observational part of the study).
One of the most well-known, longitudinal observational studies is the Framingham Heart Study (FHS). Begun in 1948 with a cohort of 5,206 men, FHS has now studied 14,000 people, including many of the children and grandchildren of the original study participants. The original goal of FHS was to understand what factors influence cardiovascular disease. To do this, the researchers performed physical examinations, conducted lifestyle interviews, gathered medical history, and ran laboratory tests every 2-6 years. This research taught us a lot about how our behaviors affect our health. The FHS demonstrated that high blood pressure, high cholesterol, specific eating habits, smoking, lack of exercise, and unhealthy weight were all key risk factors for heart disease. Knowing this fundamentally changed how we prevent and treat heart disease.
Another important example is the Baltimore Longitudinal Study of Aging (BLSA), which was founded in 1958 to understand the aging process in healthy, active people. Every 1-4 years, participants receive comprehensive health, cognitive, and functional assessments. Thanks to the thousands of people who participate in the BLSA, researchers have been able to document the progression of age-related change in all major anatomical systems as well as changes in our neurological health, including memory and cognition. Critically, BLSA identified that people could positively influence aging by making lifestyle changes, including eating well, exercising, and having an active social life.
One more longitudinal observational study worth highlighting is the Women’s Health Initiative (WHI). This study uses a combined approach to study some major diseases that affect older women. A total of 161,808 women have been enrolled in the study. Some were part of an interventional study. They received hormone replacement therapy, calcium/vitamin D supplementation, and/or a specific dietary regime. Others were part of an observational study with no intervention. By comparing these two groups, the researchers learned how various factors affected the women’s risk of major diseases. The findings from WHI have been used to modify recommendations for how and when hormone replacement therapies are used.
The Dog Aging Project is a long-term study, and like the Women’s Health Initiative, it includes both a longitudinal observational study and an interventional study, called TRIAD. Like the Baltimore Longitudinal Study of Aging, one goal of the Dog Aging Project is to develop a better understanding of just what healthy aging looks like in dogs. For example, in humans simple tests like how long it takes an elderly person to stand up from a chair or the strength of their grip indicate levels of healthy aging. We will be developing similar metrics for dogs. Another goal of the Dog Aging Project is to identify factors that will increase our dogs’ quality of life as they age. Like the Framingham Health Study, our project will study specific age-related illnesses like heart disease in great detail.
The power of the Dog Aging Project, like the other longitudinal observational studies described here, comes from (1) following large numbers of participants, (2) measuring many different variables (physical, genetic, behavioral, lifestyle, and environmental data), and (3) evaluating how these variables change over time. The connections we are able to make and the insights we are able to draw from this research will be used to find ways to increase healthspan, the period of life spent free from disease. Ultimately, increased quality of life for dogs and their humans will come through the power of paying attention.