SLEEP REGULARITY: IMPORTANT! FOR ATHLETES?

Almost sundown.Taken by PKSenagore October 24, 2012. all rights reserved.

A headline article on Fatherly.com by Joshua A. Krisch exclaims, “Adult Bedtimes: Why Kids and Parents Both Need Regular Sleep” came to attention the same day the American Medical Association “Morning Rounds” newsletter issued a blurb about the research study findings discussed in Krisch’s article.
 
The full PDF article is available online, FREE,  a signal the medical research establishment thinks the new information is important and worth disseminating to anyone who is interested. Ordinarily, medical journals release an article abstract at no cost but require a costly subscription for access to the entire publication.
 
After reading just a bit of what was learned in this study, it’s no wonder there’s excitement. The short version of the research results is that by NOT establishing a regular sleep pattern (i.e. the same bedtime and wake-up time each night/day) you may be placing yourself at increased risk for developing conditions like metabolic syndrome, hypertension, diabetes, and obesity, which increase chances of artherosclerotic cardiovascular disease, including heart attacks and stroke.  The converse seems to be true, that a regular sleep time may be protective.
 
There are not too many changes that can be made in life which promise to boost health with so little pain as this one! Difficulty and inconvenience perhaps, but not physical pain.
 
So how is sleep regularity research related to fitness?  The study came nowhere near to making this claim, but Earned Runs is proposing that possibly athletic performance in training and competition can be enhanced by increased sleep regularity!
 
Sleep has been identified as necessary for recovery from intense workouts and for muscle building. The emphasis has been on increasing total duration of sleep time and avoiding disruption, but not on regularity.  A 2017 article discusses the “Value of sleep on athletic performance, injury and recovery in the young athlete”.  It is a review of others' work rather than original research, and does not differentiate sleep regularity from other aspects of sleep at this age. Thus the Lunsford-Avery et al study, the impetus for this blog (see in italics  below), breaks new ground with their effort.

The study revealed that sleep regularity correlated with specific measures of cardio-metabolic health in the research participants, but not total duration of sleep.
 
Earned Runs thinks It’s worth trying on an individual level.   What's there to lose? If setting a regular sleep time doesn’t significantly boost speed, power, or other performance measures, perhaps it will assist with improving metabolic status and efforts to maintain lean muscle mass and reduce dangerous abdominal/visceral (belly) fat.

The findings with regard to perceived stress and self-reports of depression suggest there’s a chance that motivation and perseverance can be helped by regular bedtime and wake-up schedules.  Persistence in adhering to a training program and greater levels of enthusiasm in workouts may indirectly enhance performance.
 
The details of medical research are sometimes tedious but can add more to our understanding of the limitations of human scientific investigations.  We can rejoice in new findings but also realistically temper our enthusiasm by learning how study results were obtained.

Below are some of the details, of this sleep regularity work:
 
THE STUDY: Scientist authors Jessica Lunsford-Avery of Duke University and colleagues published an article, “Validation of the Sleep Irregularity Index in Older Adults and Association with Cardio-metabolic Risk,” describing the results of their research on sleep.  The group's 1st study goal was to determine whether a novel measure of sleep regularity (SRI) that had been recently developed, using a small group of young college students with limited racial/ethnic and socio-economic diversity, would assess sleep in a similar fashion in a larger group of older adults with various backgrounds.
 
The researchers' 2nd goal was to “examine the relationships between the SRI and cardio-metabolic risk” projected over 10 years.
 
Their reasoning was that because disturbance of or insufficient duration of sleep confers risk for the development of cardiovascular diseases and for “greater diabetes, hypertension, obesity, fasting glucose, and hemoglobin A1c status”, information on the regularity of sleep captured by the SRI might further identify others at risk for these conditions.
 
In addition, they sought to examine the effect of sleep regularity on perceived stress and depression, as “psychiatric factors tied to cardio-metabolic disease”. 
 
The authors predicted their study would demonstrate SLEEP IRREGULARITY, “as measured by the SRI”, would be associated with:
- 10-year risk of cardiometabolic disease
- greater body mass index (BMI), hypertension, fasting blood glucose, and hemoglobin A1c
- symptoms of depression and perceived stress
 
Because the scientists realized that adults older than college age have different time pressures of working and possibly family responsibilities, and some may be retired and without fixed schedules, they sought to confirm that the Sleep Regularity Index (SRI) tool could reliably be used with other populations. Specifically persons in an older age group at risk of developing cardiometabolic diseases.
 
For the current project, data from the MESA Study (Multi-Ethnic Study of Arteriosclerosis) was utilized.  MESA participants had been enrolled from 4 racial/ethnic groups (African –American, Chinese-American, Caucasian, and Hispanic), across 6 regions* of the US, and had received baseline assessments between years 2000 – 2002 (ages ranging from 45-84 years at enrollment, mean ~69 years).  Subsequent follow-up evaluations for cardiovascular and metabolic disease prevalence and cardiovascular disease risk factors**, and psychiatric health*** were performed roughly 10 years later.

A group of 1978 adults had also completed the MESA Ancillary Sleep Study between 2010-2012 (now aged 54-93) and were without evidence of sleep issues.  It was this MESA subset, for which actigraphy measures and self-reports measuring daytime-sleepiness and diurnal preferences (“morningness” or “eveningness”) were available, that was studied by Lundsford-Avery and her group.
 
“The Sleep Regularity Index (SRI)”, the authors explained, “was originally described as the likelihood that any two time-points (minute to minute) 24 hours apart were the same sleep/awake state, across all days”.      In the study, participants completed a sleep diary and wore an ActiWatch Spectrum (Philips Respironics) wrist device for 7 consecutive days.  Sleep/wake indices, physical activity, and ambient light exposure data were collected, aggregated in 30 second “epochs,” then manually scored as wake or sleep based on the sleep diary, activity and ambient light information, and an event marker on the device that subjects pressed when going to bed and rising.
 
RESULTS: SRI scores ranged between 6 and 97 points (mean ~71 points). High scorers, above the 80%ile (>84 points), identified the regular sleepers, lower scorers, below the 20%ile (<60.5 points) the irregular sleepers. There were no significant differences between sleepers who worked and those who did not, men versus women, young age versus old.
 
Among the ethnic/racial groups there were differences: African American tended to score lower compared with all other groups, and Hispanics lower than Caucasians.
 
Sleep REGULARITY WAS

• NOT associated with sleep duration
• NEGATIVELY correlated with sleep midpoint (later to bed= less regular sleep)
• NEGATIVELY correlated with daytime sleepiness
• POSITIVELY associated with greater physical activity
• POSITIVELY associated with light exposure; regular sleepers had 48.2 more min/day
• POSITIVELY correlated with “morningness” diurnal preference over “eveningness”

These findings are consistent with those of Philips who developed the SRI measure using college students, which validated the use of this measure in older adults of diverse ethnic/racial backgrounds. Study goal number 1 was accomplished!
 
IRREGULAR SLEEP was NOT associated with sleep duration, but with:
- Delayed sleep timing
- More sleep time in daylight hours (65 more minutes), less in night hours (59 less minutes)
- Increased daytime sleepiness
- Reduced physical activity and light exposure
- 10-year risk of ASCVD (atherosclerotic cardiovascular disease)
- Greater obesity, hypertension, fasting glucose, Hemoglobin A1C, and diabetes status
- Increased perceived stress and depressive symptoms
- SRI score was significantly LOWER (meaning irregular sleep) among participants with metabolic syndrome. diabetes, hypertension, and obesity
- ASCVD risk was not correlated with Total Sleep Time (TST); sleeping longer was not protective.

The 2nd study goal had been accomplished, and the research group's hypotheses had been confirmed!

The study results do not imply causation, the authors caution.  But they do raise awareness that not all sleep is equal when it comes to benefiting health.  That longer is not necessarily protective. And remind us that, just as the Fatherly.com article admonishes parents, it's not just growing babies and children that need to set need regular bedtimes. 

Today, healthy fit persons not yet worried about developing cardiovascular and metabolic diseases  might consider establishing a habit of regular sleep times to improve their athletic lives. Twenty -forty years later, they may be able to congratulate their younger selves on this wise move.

RUN & MOVE HAPPY!

*MESA data collection sites included Wake Forest University, Northwestern University, University of Minnesota, Columbia University, Johns Hopkins University, University of California at Los Angeles. 

** Systolic and diastolic blood pressure measurement and hypertension treatment status; serum low-and high-density lipoprotein cholesterol and triglyceride levels; diabetes risk by fasting blood glucose levels, metabolic syndrome as defined by 2004 NCEP guidelines, hemoglobin A1c, body mass index, obesity (BMI > 30kg/m2); coronary artery disease, prior myocardial infarction, coronary re-vascularization procedure, angina, or congestive heart disease; prior stroke or transient ischemic attack; deep vein thrombosis or pulmonary embolism. Among participants free of CVD, 10-year risk of ASCVD was calculated based on demographics, blood pressure and cholesterol measurement, and medical history

***Participants psychiatric health  was assessed using the 201-item CES-D (Center for Epidemiologic Studies Depression Scale) for depressive symptoms, and with the 4 item PSS-4 (Perceived Stress Scale) for perceived stress.

https://www.fatherly.com/health-science/adult-bedtimes-regular-sleep-patterns-science/
 
https://www.nature.com/articles/s41598-018-32402-5
 
http://www.actigraphy.com/solutions/actiwatch/actiwatch-pro.html
 
https://pdfs.semanticscholar.org/bed9/2e978f5bca851a79b16d8499b8ca21eeb3d6.pdf
 
https://www.healio.com/pediatrics/journals/pedann/2017-3-46-3/%7B3bacbe58-eeb0-45b2-bd94-54a6f8dffaa3%7D/the-value-of-sleep-on-athletic-performance-injury-and-recovery-in-the-young-athlete#divReadThis
 
https://www.healthychildren.org/English/healthy-living/oral-health/Pages/Brush-Book-Bed.aspx