Now a study by Crump and colleagues published in JAMA Intern Medicine suggests that some of this risk may be mitigated by increased physical fitness.
The cohort study involving over 1.5 million Swedish young men in Sweden, who underwent standardized aerobic capacity, muscular strength, and BMI measurements obtained at a military conscription examination and were followed for up to 40 years.
Almost 100,000 men went on to develop hypertension, whereby both high BMI and low aerobic capacity (but not muscular strength) were associated with increased risk of hypertension, independent of family history or socioeconomic factors.
A combination of high BMI (overweight or obese vs normal) and low aerobic capacity (lowest vs highest tertile) was associated with the highest risk of hypertension.
The association with aerobic fitness was apparent at every level of BMI.
Form this study the authors conclude that high BMI and low aerobic capacity in late adolescence are associated with higher risk of hypertension in adulthood.
Although one must also be cautious in assuming causality with regard to associations found in such studies, the observations are certainly compatible with the notion that increased cardiorespiratory fitness may well mitigate some of the impact of increased BMI on hypertension risk.
One factor accounting for this may well be the lack of timely access to sleep testing.
Now, a study by Hirsch Allen and colleagues from the University of British Columbia Hospital Sleep Clinic, published in the Annals of the American Thoracic Society, examined the relationship between severity of sleep apnea and travel times to the clinic in 1275 patients referred for suspected sleep apnea.
After controlling for a number of confounders including gender, age, obesity and education, travel time was a significant predictor of OSA severity with each 10 minute increase in travel time associated with an apnea-hypopnea-index increase of 1.4 events per hour.
The most likely explanation for these findings is probably related to the fact that the more severe the symptoms, the more likely patients are to travel longer distances to undergo a sleep study.
Thus, travel distance may well be a significant barrier for many patients accounting for a large proportion of undiagnosed sleep apnea – at least for milder forms.
Given the often vast distances in Canada one can only wonder about just how much sleep apnea goes under diagnosed because of this issue.
Any follower of media reports or even research papers on the relationship between obesity and mortality should be righty confused by now.
Not only are there publications suggesting that the relationship between obesity and mortality isn’t that strong after all and that perhaps the BMI levels associated with the longest survival are somewhere around 30 (and not below 25) but then there is the issue of the obesity paradox, or the finding that among people with chronic (and some acute illnesses), a higher BMI is associated with better survival than being of “normal” weight.
On the other hand, there is overwhelming evidence that higher BMI’s are associated with an increased risk of a wide range of health problems – from diabetes to cancer.
This is not to say that everyone with a higher BMI is sick – they are not! But there is no doubt that the risk of illness does increase with higher BMIs.
In our own study on the Edmonton Obesity Staging System (EOSS), which classifies individuals based on their actual health rather on their BMI, we found that while about 50% of individual in the BMI 25-30 range can be considered healthy (EOSS Stage 0 or 1), this number drops to below 15% for individuals in the BMI 40+ range.
So, if obesity is such a risk factor for disease, why do epidemiological studies struggle to consistently show an effect of obesity on mortality?
Now, a paper by Andrew Stokes and Samuel Preston, published in the Proceedings of the US National Academy of Science, suggests that it is not current weight (as used in many studies) but rather the highest lifetime weight that is most clearly associated with mortality.
Their reasoning is as follows. “Intentional” weight loss in the population is rare (very few people in the general population ever consciously manage to lose a significant amount of weight and keep it off)
In contrast, “unintentional” weight loss, when it occurs is generally a bad sign. Indeed, one of the best indicators of poor prognosis (for almost any health condition) is when someone loses weight. In many cases, this “spontaneous” weight loss can precede overt illness or death by many years.
Thus, the authors argue that most of the literature on this issue is simply confounded by the confusion caused by all the people who have unintentionally lost weight due to an underlying health problem (diagnosed or undiagnosed).
As these people would be at higher risk of death, despite measuring in at a lower weight, they muddy the waters making lower BMI levels look more dangerous (or in comparison higher BMI levels look safer) than they are.
To test their hypothesis, the researcher looked at data from the US NHANES study linked to death registers using four different approaches:
Model 1: BMI measured at the time of survey (this is the method most commonly used in epidemiological studies)
Model 2: The highest reported lifetime BMI at the time of survey
Model 3: Individuals surveyed in their current BMI class who had never been heavier compared to individuals in that BMI class who reported formerly being in a higher BMI class.
Model 4: Individuals surveyed in their current BMI class compared to people who were formerly in that BMI class but had moved to a lower BMI class by the time of the survey.
In both models 1 and 2, there was a greater risk of mortality with higher BMI class, but the relationship was stronger in model 2 (highest lifetime BMI) than in model 1 (current BMI).
In model 3, there was still an increased risk with higher BMI class but within each current BMI class, risk was higher in individuals who had previously belonged to a higher BMI class.
In model 4, mortality also rose with the highest weight achieved but was markedly higher in individuals who lost weight after achieving a particular BMI category compared to those who remained at that maximum.
These findings have important implications for our understanding of the relationship between BMI and mortality.
As the authors note,
“Confining analytic attention to survey BMI alone thus sacrifices important information provided by an individual’s maximum BMI. The poor performance of the survey-only model is especially salient because models using only BMI at survey dominate the set of findings in the literature on the relation between BMI and mortality.”
The errors in not considering highest BMI are not trivial.
“33.9% of individuals in the sample who were normal weight at survey were formerly overweight, and this group had three times the prevalence of diabetes and cardiovascular disease CVD) relative to those who were in the normal-weight category at both max and survey.”
Here is how you would interpret the data,
“Disease prevalence and mortality both rise with increases in maximum BMI and rise even further for those who reach a particular maximum BMI category and then lose weight. These patterns strongly suggest that obesity raises the risk of diabetes and CVD and that, once acquired, these diseases often precipitate weight loss….Only by using weight histories can this pattern of erasure be identified and corrected.”
The use of historical data in determining risk would not be a new concept,
“The introduction of historical data in the analysis of smoking occurred more than a half century ago, when studies began to distinguish among current-, former-, and never-smokers.”
Similarly, in the context of obesity one would need to differentiate between people who currently have obesity, people who previously had obesity, and people who never had obesity.
All of this only works, because in these type of epidemiological studies, “intentional” weight loss, be it through behaviour change, medication or surgery, is so rare as to be non-existent. Virtually all weight loss seen at a population level in “unintentional” and probably related to underlying health issues.
Thus, one should not interpret these findings to mean that someone intentionally losing weight through behavioural, medical or surgical treatments is at a higher risk for mortality – the intervention studies we have on that (this cannot be studied in population studies as there are so few cases of “treated” obesity), suggest otherwise.
For clinicians, these data point to the importance of noting the highest BMI and not just current BMI – if the patient has lost weight (especially if this is not explained by obesity treatment), then this may be a high-risk patient.
Nevertheless, surgery is surgery and no decision to have major surgery should ever be taken lightly. Despite its significant positive impact on over all health and well-being (at least for the vast majority of patients), many patients may experience moderate to severe symptoms or problems they may not have had prior to surgery.
This is exemplified in a study by Bjørn Richelsen and colleagues from Denmark published in JAMA Surgery.
In their study, the researchers conducted a survey of all available patients (n=2,238), who had undergone gastric-bypass surgery in the Central Denmark Region between January 1, 2006, and December 31, 2011.
Their responses were compared to those of 89 individuals matched for sex and body mass index.
Among the 1429 (63.7%) patients who responded to the survey, 1394 (87.4%) reported that their well-being was improved after surgery, while only 113 (8.1%) reported reduced well-being.
However, almost 90 % of patients reported 1 or more symptoms after surgery, which were serious enough for 70% of them to contact their health care system.
Almost 30% of all patients had to be hospitalized in the 4.7 years of follow-up, compared to only 7% in the control group.
The most common problems leading to health care contact were abdominal pain (34.2%), fatigue (34.1%),
and anemia (27.7%).
Women, patients younger than 35, smokers, unemployed persons and those with surgical symptoms before surgery, were at greatest risk for symptoms.
Thus, although the vast majority of surgical patients reported that their health and well-being was better than before surgery, the vast majority also had symptoms for which many were hospitalized.
While these data may be an overestimate (given that less than 65% of eligible patients responded to the survey), and one may perhaps argue that patients with symptoms were perhaps more likely to respond, there is little doubt that many (if not most) people undergoing gastric-bypass surgery will have some symptoms related to surgery.
No doubt, there appears room for improvement as far as surgery is concerned.
Bottom line: severe obesity remains a difficult disease to treat and our current treatments are far from perfect.
This is even more true for children with physical disabilities, who face even greater challenges when it comes to preventing or managing excessive weight gain. Unfortunately, not much is known about the extent of this problem or possible solutions.
Now a group of Canadian experts in paediatrics and rehabilitation have put out a Call to Action, published in Childhood Obesity, for a research agenda that focuses on this important sub-group of kids.
The call is the result of a Canadian multistakeholder workshop on the topic of obesity and health in children with physical disabilities that was held in October 2014.
The participants in the workshop included researchers, clinicians, parents, former clients with disabilities, community partners, and decision makers.
Given the paucity of research in this area, it is not surprising that the participants identified over 70 specific knowledge gaps that fell into 6 themes: (1) early, sustained engagement of families; (2) rethinking determinants of obesity and health; (3) maximizing impact of research; (4) inclusive integrated interventions; (5) evidence-informed measurement and outcomes; and (6) reducing weight biases.
Within each theme area, participants identified potential challenges and opportunities related to (1) clinical practice and education; (2) research (subareas: funding and methodological issues; client and family engagement issues; and targeted areas to conduct research); and (3) policy-related issues and topic positioning.
Recommendations emerging from the workshop’s multistakeholder consensus activities included:
Children’s and families’ needs must be integrated into prevention and treatment programs, taking into account the additional caring commitments and environmental challenges often experienced by families of children with physical disabilities. Guidelines need to be developed regarding how best to engage children/families meaningfully in designing both clinical interventions and health promotion research initiatives.
Research in obesity and health in children with physical disabilities should be guided by a conceptual model, determining both common and unique determinants of health and obesity compared with their typically developing peers. A conceptual model enables existing knowledge about obesity prevention and management from other populations to be integrated into approaches for children with physical disabilities where appropriate, as well as the identification of areas where disability-specific knowledge is still needed. It is critical that any such model incorporates social and environmental factors that can affect both weight and health, rather than locating responsibility within the individual by default.45 The alignment of our model with the ICF ensures that our approach remains truly biopsychosocial.
Valid, reliable, clinically appropriate, and acceptable outcome measures are urgently needed in order to monitor children’s weight and health, and identify overweight and obesity, where conventional outcomes (e.g., BMI) alone have been shown as suboptimal.
As the authors note,
“Canadian researchers are now well positioned to work toward a greater understanding of weight-related topics in children with physical disabilities, with the aim of developing evidence-based and salient obesity prevention and treatment approaches.”
Hopefully, they will now find the funding required to do the work.