While research has shown that moderate to vigorous physical activity improves blood sugar levels for adults who are at higher risk of developing insulin resistance (often a precursor to prediabetes or type 2 diabetes), this new study adds to growing evidence that the greatest benefits may come from moving more later in the day.[2]The new study shows that it’s not just the amount of physical activity, but that timing is also relevant when improving blood sugar control, says coauthor Antonio Clavero Jimeno, a PhD candidate at the Sport and Health University Research Institute at the University of Granada in Spain.“Our findings emphasize the significance of precision exercise prescription. Certified sports and medical personnel should consider the optimal timing of the day to enhance the effectiveness of the exercise and physical activity programs they prescribe, especially for people at higher risk of developing insulin resistance and type 2 diabetes,” says Jimeno.Physical Activity at Night Is Better at Lowering Daytime Blood Sugar LevelsThe study included 186 participants with an average age of 46 and an average BMI of 33. Investigators monitored physical activity and glucose patterns over a 14-day period using a wristband activity tracker and a continuous glucose-monitoring device.The amount and timing of daily moderate to vigorous physical activity were recorded, and participants were grouped according to when people were the most active.Examples of moderate activity include brisk walking, dancing, and gardening, and vigorous intensity activities include jogging, running, fast cycling, fast swimming, and walking briskly up a hill.[3]Researchers found that getting 50 percent or more of daily moderate to vigorous activity in the evening was associated with lowering day, night, and overall blood glucose levels compared with being inactive, and the link was stronger in people with impaired glucose regulation.“The results show slightly greater reduction in blood glucose levels if exercise is performed in the late afternoon or evening, but the difference is minimal compared to the mixed and morning exercise [groups],” says Malene Lindholm, PhD, an instructor of cardiovascular medicine and researcher at Stanford University in California, who was not involved in the research.These findings confirm what Fatima Syed, MD, an internal medicine doctor who specializes in diabetes and weight management at Duke Health in Durham, North Carolina, sees in her practice.For managing blood sugar levels, exercising in the evening, and particularly after dinner, can improve morning glycemic control, says Dr. Syed.Managing Blood Sugar Important for Health and Weight ManagementBlood sugar regulation is extremely important for many aspects of health, including weight control, says Dr. Lindholm.“Maintaining stable blood sugar levels helps the body regulate energy storage and utilization. High blood sugar stimulates insulin release, which increases fat storage, and high blood sugar for longer periods of time may lead to insulin resistance,” she says.Insulin resistance is when the cells in your body don’t respond well to insulin, which is the hormone that’s released when blood sugars rise after eating. It lowers bloods sugar and helps glucose (your body’s main energy source) enter cells in the liver, fat, and muscle.When a person has insulin resistance, it takes more insulin to get the job done. It isn’t the same as prediabetes or diabetes, but you have to have insulin resistance before you are diagnosed with either.[4]“Insulin resistance is a vicious cycle. The way to improve it is to lose weight, but it makes it harder to lose weight. Reducing insulin resistance, as measured by better blood sugar control, helps with weight loss,” says Syed.Why Would After-Dinner Exercise Be More Beneficial?These findings add support to the benefits of evening exercise. An Australian study published earlier this year found that doing the majority of moderate to vigorous physical activity in the evening was associated with the greatest reductions in death and heart disease.[5]But why would evening be the best time to be active?“When we eat, particularly when we eat carbohydrates, our bodies need to process that food and send glucose into cells. Diseases of insulin resistance, like obesity or metabolic syndrome, make it harder for glucose to go where it needs to be,” explains Syed.But exercise lowers insulin resistance, and therefore lowers glucose levels, she says.“It makes sense evening exercise would be helpful, because when we sleep our body releases glucose to regulate our blood sugars, and if we reduce insulin resistance, glucose goes into the cells they belong in, instead of remaining in the bloodstream,” she says.The benefits may relate to circadian rhythms or changes in insulin sensitivity through the day. Physical activity may compensate for worsening insulin sensitivity at night, for example, says Sun Kim, MD, an endocrinologist at Stanford Health Care in California.Previous research has shown that there is a circadian rhythm to insulin sensitivity. Scientists believe that insulin sensitivity during evening hours was developed to protect against low blood sugar throughout the night.[6]It could also be related to what people are not doing because they’re being more active, says Dr. Kim. “For example, individuals who are more physically active at night may eat earlier or eat less than those who are not physically active or exercise earlier in the day. Diet information is not given in this study,” she says.Bottom Line: The Best Time to Exercise Is Whenever You Can“My message is to find a time that works for exercise. Most of my patients with type 2 diabetes struggle to find any time to exercise,” says Kim.Based on these findings, if a person has the luxury to pick a time, they can consider the evening, she says.This study and other research indicates that it may be that people with impaired glucose tolerance benefit slightly more from exercise later in the day compared to morning, but Lindholm believes there’s still not enough evidence to recommend it over morning exercise.“People should exercise whenever they have time and opportunity to maximize the beneficial health effects. The exercise that gets done is the most beneficial,” she says.