NEW ORLEANS — Walking downhill on a treadmill within an hour after eating produced a large osteogenic response in postmenopausal women with diabetes — an effect not seen with uphill walking, a researcher said here.
In a randomized, partial-crossover trial, women who exercised downhill for 40 minutes had increased levels of C-terminal propeptide of type I collagen (a marker of bone formation) relative to no-exercise control and to walking uphill, reported Katarina Borer, PhD, of the University of Michigan, and colleagues.
Women exercising downhill also had reduced insulin resistance to high-carbohydrate meals compared to women exercising uphill or sedentary women, demonstrated by Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) scores, she reported here at ENDO 2019, The Endocrine Society meeting.
“Even if you are postmenopausal and you have low estrogen, or you’re diabetic and your bones are more fragile, the bone is still alive and is responding to exercise,” Borer told MedPage Today. “But not any exercise, at any time, and not regardless of your prandial state.”
In this study, 15 women were assigned to participate in two of five experimental conditions: no exercise, walking uphill before a standardized meal, walking uphill after the meal, walking downhill before the meal, and walking downhill after the meal, on a treadmill that could be tilted upward or downward as desired. Borer and colleagues created an “osteogenic ratio,” which they defined as the level of CICP over the level of c-terminal telopeptide of type I collagen (CTX), a marker of bone resorption.
As expected, women assigned to walk uphill exerted a greater mean effort than women in the downhill group (75.2% vs 47.9%), whereas the downhill condition created a 38% greater strike force as measured with a shoe insert. This increased mechanical loading helps mitigate the loss of bone mass, Borer said.
“Intuitively you’d think you’re working harder going uphill and that it’s going to be more beneficial, but actually you are unloading the bones because you’re working against gravity,” Borer said.
Among women who walked downhill, exercising after the meal increased CICP by 44% and was linked to a 40% greater osteogenic ratio compared to exercising before the meal, researchers reported. In all women, the meals lowered bone resorption (CTX), regardless of whether they exercised up or downhill. Exercise before eating, irrespective of uphill/downhill direction, had no observable effect on these outcomes.
Mone Zaidi, MD, PhD, of the Icahn School of Medicine at Mount Sinai in New York City, said exercise could plausibly be one of many components contributing to bone fragility in women with diabetes, but that factors more related to the women’s diabetes itself are more likely at play.
For example, the longer a patient has diabetes, the more advanced glycation end products (AGE) accumulate, he said, and the concentration of AGEs in diabetic patients are known to be associated with fracture risk. This would need to be measured and controlled for in order for Borer’s results to be interpreted with confidence, he said.
On the other hand, the timing of meals pertains to hypoglycemic episodes experienced by patients with diabetes, and would also need to be carefully evaluated in a study linking eating to bone health, he added.
“It doesn’t seem you can tease it out that easily without including the big confounders,” Zaidi told MedPage Today.
The 15 women involved in this study were a mean age of 58 years, had been menopausal for about 7 years, were diabetic (fasting glucose 137.4 mg/dL), and were overweight (mean body mass index 27.3). They were also osteopenic with a mean z-score of 1.56.