A recent study by researchers at the Northwestern University Feinberg School of Medicine found that people who reported a sense of purpose in life also tended to get better sleep regardless of confounding variables such as age, race, gender and level of education.
The researchers chose the sample for this study based on two ongoing longitudinal, epidemiological cohort studies of aging and cognition.
The two studies are the Minority Aging Research Study, a study produced for African- Americans aged 65 and older which aims to prevent poor memory and slowed walking, and the Rush Memory and Aging Project, a study on plummeting cognitive function and vulnerability to Alzheimer’s disease.
African-American people were recruited from the Minority Aging Research Study and white people were recruited from the Rush Memory and Aging Project.
None of the participants in either study were known to have dementia. They were selected from community-based organizations, churches and senior-subsidized housing facilities.
Longitudinal studies observe the same group repeatedly over a long period of time. It was important for this research to sample participants from longitudinal studies because it allowed them to compare clinical evaluations over time, thereby letting the researchers know plenty of information about the participants immediately.
Purpose in life was assessed by using a 10-item measure derived from Ryff and Keyes’ scales of Psychological Well-Being.
The Ryff inventory contains either 84 questions or 54 questions. Both the long and medium forms include a sequence of statements demonstrating the six areas of psychological well-being: autonomy, environmental mastery, personal growth, positive relations with others, purpose in life and self-acceptance.
The participants were asked to rate their agreement with statements such as “I feel good when I think of what I’ve done in the past and what I hope to do in the future,” and “Some people wander aimlessly through life, but I am not one of them.”
Based on the answers to these questions, participants were given a score between 1 and 5 with a higher number being an indication of a higher sense of purpose in life.
Sleep quality and possible presence of sleep disorders were then measured using a 32-item questionnaire derived from the Pittsburgh Sleep Quality Index, the Berlin Questionnaire and the Mayo Sleep Questionnaire.
The Pittsburgh Sleep Quality Index asks questions pertaining to sleep quality, the Berlin Questionnaire identifies sleep apnea risk and the Mayo Sleep Questionnaire concentrates on REM sleep behavior disorder.
Based off the answers to these questions, each participant was given a score from zero to 16 with higher scores indicating a poorer sleep quality.
Clinical assessments of the participants were conducted annually, which allowed the researchers to limit the effect of age on the results. The covariates of age, sex, race and years of education were accounted for by using hierarchical logistic regression analyses.
These analyses reflected variables that affected the results in a statistically significant manner.
As it turns out, the results of these analyses for this specific study indicated that the aforementioned variables were irrelevant because they did not affect the results of the study in a statistically significant manner.
The researchers determined that sleep quality is related to purpose in life, with people who reported a greater sense of purpose enjoying a better night’s sleep.
Additionally, the risk of developing sleep apnea is lower for people who have a greater sense of purpose in life.
These results could easily be expanded to reflect the general populace because of the variety of individuals involved.
However, there was one major factor that did not reflect positively on the validity of the study: the results were based solely off self-reported questionnaires. This means that the results are open to recall bias, or the idea that systematic error is caused by differences in the accuracy or completeness of the recollections retrieved by study participants regarding events or experiences from the past, as well as to subjective interpretation of sleep symptoms. There is also a subtler way that one confounding variable could have affected the study.
Level of education was directly taken into consideration, however, varying levels of education between participants of the study also generally indicate a difference in socioeconomic status. A high socioeconomic status was associated with choosing healthier lifestyles including a healthier diet and more physical exercise, even if people with greater wealth do not necessarily have a greater sense of purpose in life.
Despite these limitations, this study indicates that purpose in life, which was previously considered a social construct that had no effect on one’s biology, has a hand in one of the most important functions of the human body.
Though people may not precisely know the function of sleep, they know that lack of sleep is associated with issues such as obesity, diabetes and cardiovascular disease. Additional avenues of research have considered the link between sleep and other life constructs that may not have been previously associated with biological functions.