For the review and meta-analysis, which was published in March 2021 in Movement Disorders, researchers examined data combined from nine previous studies that followed individuals with type 2 diabetes over time to see if they developed Parkinson’s disease. They found type 2 diabetes associated with a 21 percent increased risk of Parkinson’s and with faster symptom progression. Parkinson’s causes muscle stiffness, tremors, impaired balance, and slow movement, in addition to cognitive and sleep issues, according to the National Institute on Aging. Yet study authors could not account for the severity of participants’ type 2 diabetes, and they couldn’t determine the effect of diabetes drugs or quality of blood sugar management on Parkinson’s disease risk — two major limitations. The research doesn’t prove that diabetes causes Parkinson’s, though researchers speculated the disease may contribute to this risk. They conducted a separate analysis of studies that identified common genetic variations present with the two conditions and found that type 2 diabetes directly increased the odds of developing Parkinson’s by 8 percent. “We used genetic data to examine whether associations that we saw might be causal — that is, that type 2 diabetes increases Parkinson’s risk and progression rather than just being associated for any other reason,” says the senior study author, Alastair Noyce, PhD, of the Wolfson Institute of Preventive Medicine at Queen Mary University of London in the United Kingdom. “We found some evidence to support that being the case,” Dr. Noyce says. “So, we conclude that treatment or prevention of type 2 diabetes may reduce the risk of Parkinson’s or its progression.” RELATED: What Are the Complications of Type 2 Diabetes?

How Type 2 Diabetes May Contribute to the Risk of Parkinson’s Disease

Although the analysis wasn’t designed to determine how type 2 diabetes might cause Parkinson’s disease to develop or progress, it’s possible that systemic inflammation present with type 2 diabetes may contribute to Parkinson’s disease, says Noyce. Vascular disease that develops with type 2 diabetes may also lead to impaired blood flow to the brain that hastens the development of Parkinson’s disease, hypothesizes Emanuele Cereda, MD, PhD, of the clinical nutrition and dietetics unit at Fondazione IRCCS Policlinico San Matteo in Pavia, Italy, who was not involved in the current study. Another possibility is that the same processes that cause diabetes also cause the nerve cell degeneration present in Parkinson’s disease, says Tom Foltynie, PhD, a professor of neurology at University College London in the United Kingdom. In particular, insulin resistance, the body’s inability to respond normally to the hormone insulin, may be involved in both type 2 diabetes and Parkinson’s disease, says Dr. Foltynie, who also was not involved in the current research. RELATED: Why Some Researchers Are Calling Alzheimer’s a ‘Type 3 Diabetes’

Some previous research has linked certain medications for type 2 diabetes to a lower risk of the development or progression of Parkinson’s disease. A study published in August 2017 in The Lancet found Parkinson’s disease symptoms improved in participants who took exenatide, a diabetes drug in a family of medicines known as GLP1 agonists, and worsened when subjects took a placebo. Another study, published in October 2020 in Brain, found that individuals with type 2 diabetes who took GLP1 agonists or another type of diabetes drugs known as DPP4 inhibitors had a lower risk of developing Parkinson’s disease. Slightly elevated blood sugar or variations in blood sugar may contribute to the risk of Parkinson’s disease even in people without diabetes, according to a study published in October 2020 in Diabetes & Metabolism. Age is the biggest risk factor for Parkinson’s disease, though, and genetics also account for up to 20 percent of the risk, Foltynie says. RELATED: How to Keep Your Brain Healthy: A Conversation With Sanjay Gupta, MD

What Should I Do if I’m Managing Type 2 Diabetes and Concerned About My Parkinson’s Risk?

The takeaway of the new analysis for people currently managing or caring for a person with diabetes is unclear. This specific research, for example, doesn’t illustrate how someone with diabetes may help lower their risk of Parkinson’s disease, says Dr. Cereda. “Unfortunately, although there is some evidence that diabetes is a risk factor for developing Parkinson’s disease, there is no evidence that optimal diabetes control reduces the risk of Parkinson’s disease,” says Cereda. Yet managing blood sugar is still essential for people with type 2 diabetes, because failing to do this increases the risk of a wide range of health problems including heart disease, stroke, and kidney failure, Cereda says. The study results suggest that we might one day add Parkinson’s disease to the long list of conditions that can be prevented at least in part by good diabetes management, Cereda adds. Noyce agrees, emphasizing the importance of blood sugar management regardless of potential Parkinson’s risk. “There are many other negative health outcomes that are associated with [uncontrolled] type 2 diabetes, such as heart disease, stroke, nerve and kidney damage, and visual loss,” Noyce says. “These are all more common than Parkinson’s, and the risk of these things can be reduced with treatment of diabetes, modification of diet, exercise and self-care.” According to the U.S. Centers for Disease Control and Prevention, following a healthy diet, losing weight, managing blood sugar and blood pressure, exercising regularly, and avoiding smoking are just some of the steps people with diabetes can take to help keep complications at bay. “The focus for patients right now should be on doing what they can to reduce the chance of these other negative health outcomes, while alongside that we continue to understand the link between type 2 diabetes and conditions like Parkinson’s,” Noyce says. RELATED: Diabetes Nearly Doubles the Risk of Heart Failure