As part of the University of Colorado Department of Medicine’s annual Research Day on April 23, Professor Christine Swanson, MD, MCR, described her National Institutes of Health-funded clinical research on whether adequate sleep can help to prevent osteoporosis.
“Osteoporosis can occur for many reasons, such as hormonal changes, aging and lifestyle factors,” said Swanson, associate professor in the Division of Endocrinology, Metabolism and Diabetes. “But some patients I see don’t have an explanation for their osteoporosis.
“Therefore, it is important to look for new risk factors and consider what other changes throughout life, such as bones, sleep,” he added.
How bone density and sleep change over time
In their late 20s, people reach what’s called peak bone mineral density, which is higher in men than women, Swanson said. This peak is one of the main determinants of fracture risk in the future.
After reaching this peak, a person’s bone density remains more or less stable for a couple of decades. Then, as women enter the menopausal transition, they experience accelerated bone loss. Men also experience a decrease in bone density as they age.
Sleep patterns also evolve over time. As people age, total sleep time decreases and the composition of sleep changes. For example, sleep latency, which is the time it takes to fall asleep, increases with age. On the other hand, slow wave sleep, which is deep, restful sleep, decreases as we age.
“And it’s not just the duration and composition of sleep that changes. Circadian phase preference also changes throughout life, in both men and women,” Swanson said, referring to people’s preference over when they go to sleep and when they wake up.
How can sleep be related to our bone health?
The genes that control our internal clock are present in all of our bone cells, Swanson said.
“When these cells are reabsorbed and form bone, they release certain substances into the blood that allow us to estimate how much bone turnover is occurring at any given time,” he said.
These markers of bone resorption and formation follow a daily rhythm. The amplitude of this rhythm is greater for markers of bone resorption (which refers to the process of bone breakdown) than for markers of bone formation, he said.
“This rhythmicity is likely important for normal bone metabolism and suggests that sleep and circadian disruptions could directly affect bone health,” he said.
Investigating the connection between sleep and bone health
To better understand this relationship, Swanson and colleagues investigated how markers of bone turnover responded to cumulative sleep restriction and circadian disruption.
For this study, participants lived in a completely controlled hospital environment. Participants did not know what time it was and were given a 28-hour schedule instead of a 24-hour day.
“This circadian disruption is designed to simulate the stress endured while working rotating night shifts and is roughly equivalent to flying four time zones west every day for three weeks,” he said. “The protocol also caused participants to sleep less.”
The research team measured bone turnover markers at the beginning and end of this intervention and found significant detrimental changes in bone turnover in both men and women in response to sleep and circadian disruption. Detrimental changes included decreases in bone formation markers that were significantly greater in younger people of both sexes compared to older people.
Additionally, young women showed significant increases in the bone resorption marker.
If a person forms less bone and at the same time reabsorbs the same amount, or even more, then over time that could lead to bone loss, osteoporosis and an increased risk of fracture, Swanson said.
“And sex and age could play an important role, with younger women potentially being most susceptible to the detrimental impact of lack of sleep on bone health,” he said.
Research in this area is ongoing, he added.