PLoS One: Obesity, Viral Pneumonitis & The 2009 H1N1 Pandemic

 

Photo Credit CDC PHIL

 

 

# 6936

 

Very early in the 2009 H1N1 pandemic we began to see reports (see H1N1 Morbidity And Previously Existing Conditions) of unusual numbers of obese influenza patients populating intensive care facilities around the world, raising concerns that obesity might be a significant pandemic risk factor.

 

In her address to the world announcing the declaration of the H1N1 pandemic on June 11th, (see WHO: Chan Statement On Raising Pandemic Level), Margaret Chan listed obesity as one of the pre-existing conditions that lent themselves to severe outcomes with this virus, saying:

 

“Many, though not all, severe cases have occurred in people with underlying chronic conditions. Based on limited, preliminary data, conditions most frequently seen include respiratory diseases, notably asthma, cardiovascular disease, diabetes, autoimmune disorders, and obesity.”

 

Over the next couple of months obesity, and particularly morbid obesity, was frequently mentioned as a possible risk factor, along with asthma, diabetes, and immune disorders.   

 

That is, until an ACIP meeting held at the end of July, where evidence was presented that showed that the incidence of hospitalizations among those listed as obese by their BMI was practically the same as their prevalence in society.

 

Roughly 34% of Americans are obese, and roughly 38% of those hospitalized met that criteria.    While 6% are morbidly obese (BMI > 40), they only made up 7% of the hospitalized cases.

 

At the time the CDC’s Dr. Anne Schuchat stated that the jury was still out on the morbidly obese, but there was no clear evidence that obesity – without some comorbid condition like diabetes – created a greater risk of complications from pandemic H1N1.

 

Of course, this was very early in the game, and data was sparse.

 

In September, in Study: Half Of ICU H1N1 Patients Without Underlying Conditions, it became apparent that while pre-existing risk factors were important, they were not the sole reason behind flu victims ending up in intensive care.

 

In November, Eurosurveillance Journal  published a Study: H1N1 Hospitalization Profiles, that similarly found :

 

• The most common risk factor in admission to intensive care was chronic respiratory disease followed by chronic neurological disease, asthma and severe obesity.
• 51% of hospitalized cases and 42% of ICU cases were not in a recognized risk group.

 

This back-and-forth reporting on the significance of obesity as a risk factor continued, which I covered in blogs including:

 

NIH: Post Mortem Studies Of H1N1

Study: Quantifying H1N1 Risk Factors

Morbid Obesity And H1N1 Flu

 

In March of 2010, the CDC (in response to a recently published PLoS One study), posted the following:

 

What has been learned from the 2009 H1N1 pandemic about obesity and risk of serious influenza disease death?

During the 2009 H1N1 pandemic, early reports from the United States and abroad suggested that obesity was more frequent among persons hospitalized with 2009 H1N1 disease or who died following 2009 H1N1 infection.

 

Since that time, a number of studies have suggested that many 2009 H1N1patients tend to be morbidly obese. The study “Morbid Obesity as a Risk Factor for hospitalization and Death due to 2009 Pandemic Influenza A (H1N1) Disease,” published in PLoS ONE, sought to determine whether or not obesity or morbid obesity were in fact independent risk factors for serious 2009 H1N1-related complications, including death.  This study found that morbidly obesity persons have a higher risk of hospitalization for 2009 H1N1 infection compared to persons with normal weight. Data from this study also suggest that the risk of death following H1N1 infection may be higher for morbidly obese individuals.

 

As more data was gathered analyzed, it was becoming apparent that morbid obesity (BMI > 40) was associated with a greater risk from pandemic flu. 

 

In early 2011 (see Extreme Obesity: A Novel Risk Factor For A Novel Flu) the IDSA’s journal Clinical Infectious Diseases carried a study called  A Novel Risk Factor for a Novel Virus: Obesity and 2009 Pandemic Influenza A (H1N1), that found:

 

Extreme obesity associated with higher risk of death for 2009 H1N1 patients

[EMBARGOED FOR JAN. 5, 2011] For those infected with the 2009 pandemic influenza A (H1N1) virus, extreme obesity was a powerful risk factor for death, according to an analysis of a public health surveillance database. In a study to be published in the February 1, 2011, issue of Clinical Infectious Diseases, researchers associated extreme obesity with a nearly three-fold increased odds of death from 2009 H1N1 influenza. Half of Californians greater than 20 years of age hospitalized with 2009 H1N1 were obese. 

 

All of which serves as prelude to a new study that appears in PLoS One today called:

 

Viral Pneumonitis Is Increased in Obese Patients during the First Wave of Pandemic A(H1N1) 2009 Virus

Jen Kok, Christopher C. Blyth, Hong Foo, Michael J. Bailey, David V. Pilcher, Steven A. Webb, Ian M. Seppelt, Dominic E. Dwyer, Jonathan R. Iredell

Introduction

There is conflicting data as to whether obesity is an independent risk factor for mortality in severe pandemic (H1N1) 2009 influenza (A(H1N1)pdm09). It is postulated that excess inflammation and cytokine production in obese patients following severe influenza infection leads to viral pneumonitis and/or acute respiratory distress syndrome.

Methods

Demographic, laboratory and clinical data prospectively collected from obese and non-obese patients admitted to nine adult Australian intensive care units (ICU) during the first A(H1N1)pdm09 wave, supplemented with retrospectively collected data, were compared.

Results

Of 173 patients, 100 (57.8%), 73 (42.2%) and 23 (13.3%) had body mass index (BMI) <30 kg/m², ≥30 kg/m² (obese) and ≥40 kg/m² (morbidly obese) respectively.

Compared to non-obese patients, obese patients were younger (mean age 43.4 vs. 48.4 years, p = 0.035) and more likely to develop pneumonitis (61% vs. 44%, p = 0.029).

Extracorporeal membrane oxygenation use was greater in morbidly obese compared to non-obese patients (17.4% vs. 4.7%, p = 0.04). Higher mortality rates were observed in non-obese compared to obese patients, but not after adjusting for severity of disease.

C-reactive protein (CRP) levels and hospital length of stay (LOS) were similar. Amongst ICU survivors, obese patients had longer ICU LOS (median 11.9 vs. 6.8 days, p = 0.017). Similar trends were observed when only patients infected with A(H1N1)pdm09 were examined.

Conclusions

Among patients admitted to ICU during the first wave of A(H1N1)pdm09, obese and morbidly obese patients with severe infection were more likely to develop pneumonitis compared to non-obese patients, but mortality rates were not increased. CRP is not an accurate marker of pneumonitis.

 

Interestingly, what these researchers found was a mixed bag.  While obesity was linked to a higher incidence of pneumonitis, somewhat surprisingly it was not linked to a higher rate of mortality.

 

The authors write:

 

In the present study, obesity was an independent predictor of pneumonitis after adjusting for age and chronic lung disease. Furthermore, clinicians may have intervened with more advanced levels of respiratory support in the obese patients pre-emptively and more readily prior to even more significant respiratory failure.

 

Although our obese patients were more likely to develop pneumonitis, they were also more likely to recover once the acute lung insult resolved.

 

The duration of mechanical ventilation was similar between obese and non-obese patients, comparable to the experience of critically ill patients with respiratory failure prior to the 2009 pandemic

 

The entire research article is very much worth reading, but the authors end by writing:

 

In conclusion, obese patients with severe A(H1N1)pdm09 infection from the first pandemic wave in Australia were more likely to develop pneumonitis compared to non-obese patients, but mortality rates were similar between the two groups after adjusting for severity of disease.

 

Although there is on-going debate as to whether obesity is a risk factor for severe A(H1N1)pdm09 infection, annual influenza vaccination should be prioritized in this group given the increased risk of serious complications from seasonal influenza infection

 

Nearly 4 years after the initial outbreak of novel H1N1, research on this most-studied pandemic of all time continues. The massive amount of data collected during the 2009-2012 pandemic has not yet been fully explored, and will undoubtedly fuel many more studies for years to come.

JAMA: BMI And All Cause Mortality

Photo Credit CDC PHIL

 

# 6816

 

*** UPDATED ***

This study, which I knew would be controversial, has sparked serious rebukes from some members of the medical community. In the Interest of fairness, here is a link to an article from BBC News, where a number of doctors take issue with its findings.

 

'Weight is healthy' study criticised

A study which suggests being overweight can lead to a longer life has caused controversy among obesity experts.

(Continue . . . )

************************

 

 

As someone who has been `gravitationally challenged’ nearly all of his life, I naturally have concerns that my extra poundage may be cutting into my lifespan.

 

While aesthetically, thinner may be perceived by many as being better, increasingly we are seeing evidence to suggest that carrying a few extra pounds may actually extend one’s lifespan, not shorten it.

 

Last October, in Studies Weigh In On The `Obesity Paradox’, we looked at research that suggested that for people with certain medical conditions, including diabetes, congestive heart failure, kidney dialysis, heart attacks, and Asthma - carrying some extra weight appears to improve their outcomes

 

Now, in a study published in JAMA, we have the most comprehensive look to date at all-cause mortality spanning nearly 3 million people (and 270,000 deaths), and sorted by BMI (Body Mass Index) classification.

 

Photo Credit JAMA Report Video

 

The results, consistent across all ages and ethnic groups, indicated that while BMI’s over 35 (Class 2 and Class 3 obesity) increase overall mortality, that simply being overweight (BMI 25-<30) was associated with a significant reduction in all-cause mortality.

 

And even those who fell into the next higher BMI category (class 1 obesity) saw a 5% reduction in overall mortality compared to those falling into the normal weight BMI (18.5-<25).

 

Mortality rates do jump considerably once you reach a BMI > 35 ( resulting in a 29% increased risk of death for obesity grades 2 and 3). The HHS maintains an online BMI calculator HERE, where you can input your height and weight and quickly find out your number.

 

The JAMA article, which is heavy in statistics and details, is freely available at the following link.

 

Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories: A Systematic Review and Meta-analysis

Katherine M. Flegal, PhD; Brian K. Kit, MD; Heather Orpana, PhD; Barry I. Graubard, PhD

Conclusions and Relevance  Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality. The use of predefined standard BMI groupings can facilitate between-study comparisons.

 

Several brief videos, and press release (excerpts below) can be viewed at:

 

Higher Levels of Obesity Associated With Increased Risk of Death; Being Overweight Associated With Lower Risk of Death

EMBARGOED FOR RELEASE: 3 P.M. (CT) TUESDAY, JANUARY 1, 2013

CHICAGO – In an analysis of nearly 100 studies that included approximately 3 million adults, relative to normal weight, overall obesity (combining all grades) and higher levels of obesity were both associated with a significantly higher all-cause risk of death, while overweight was associated with significantly lower all-cause mortality, according to a study in the January 2 issue of JAMA.

 

“Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting,” according to background information in the article.

 

Katherine M. Flegal, Ph.D., of the National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Md., and colleagues conducted a study to compile and summarize published analyses of body mass index (BMI) and all-cause mortality that provide hazard ratios (HRs) for standard BMI categories. For the review and meta-analysis, the researchers identified 97 studies that met inclusion criteria, which provided a combined sample size of more than 2.88 million individuals and more than 270,000 deaths. Regions of origin of participants included the United States or Canada (n = 41 studies), Europe (n = 37), Australia (n = 7), China or Taiwan (n = 4), Japan (n = 2), Brazil (n = 2), Israel (n = 2), India (n = l), and Mexico (n = l).

 

All-cause mortality HRs for overweight (BMI of 25-<30), obesity (BMI of ≥30), grade 1 obesity (BMI of 30-<35), and grades 2 and 3 obesity (BMI of ≥35) were calculated relative to normal weight (BMI of 18.5-<25).

 

The researchers found that the summary HRs indicated a 6 percent lower risk of death for overweight; a 18 percent higher risk of death for obesity (all grades); a 5 percent lower risk of death for grade 1 obesity; and a 29 percent increased risk of death for grades 2 and 3 obesity.

 

The authors note that the finding that grade 1 obesity was not associated with higher mortality suggests that that the excess mortality in obesity may predominantly be due to elevated mortality at higher BMI levels.

(Continue . . . )

 

In an accompanying editorial, Does Body Mass Index Adequately Convey a Patient’s Mortality Risk?, authors Steven B. Heymsfield, MD and William T. Cefalu, MD write:

 

The presence of a wasting disease, heart disease, diabetes, renal dialysis, or older age are all associated with an inverse relationship between BMI and mortality rate, an observation termed the obesity paradox or reverse epidemiology. The optimal BMI linked with lowest mortality in patients with chronic disease may be within the overweight and obesity range. Even in the absence of chronic disease, small excess amounts of adipose tissue may provide needed energy reserves during acute catabolic illnesses, have beneficial mechanical effects with some types of traumatic injuries, and convey other salutary effects that need to be investigated in light of the studies by Flegal et al and others.”

 

“Not all patients classified as being overweight or having grade 1 obesity, particularly those with chronic diseases, can be assumed to require weight loss treatment. Establishing BMI is only the first step toward a more comprehensive risk evaluation.”

 

While I can think of many other disadvantages to being overweight (my dreaded fear of wicker furniture being one), it appears that at least in terms of overall mortality - carrying a few extra pounds may actually turn out to be desirable - particularly among those who have chronic ailments.

Studies Weigh In On The `Obesity Paradox’

 

Photo Credit CDC PHIL

 

 

# 6651

 

While just about everyone will concede that being lean and athletic is preferable to being soft and pudgy, there is a growing body of evidence that – with some medical conditions, at least - having a bit of extra poundage could be beneficial to your long-term survival. 

 

Research has shown that patients having a BMI > 30 actually are more likely to survive certain medical conditions than patients with a normal or below-normal body mass index.

 

It’s called the `Obesity Paradox’, and quite frankly, it’s been driving doctors and researchers just a little bit nuts for years.  

 

Now, before anyone cries `foul’, there are plenty of health risks that come from being obese, including diabetes, coronary artery disease, sleep apena, hypertension, and stroke. The point here isn’t that being overweight is healthier.

 

it isn’t.

 

But for people with certain medical conditions, including diabetes, congestive heart failure, kidney dialysis, heart attacks, and Asthma - carrying extra pounds appears to improve their outcomes.

 

This curious (and controversial) finding was first described in the literature in 1999, regarding survival rates of patients on kidney dialysis (see Influence of excess weight on mortality and hospital stay in 1346 hemodialysis patients). 

 

Since then, this phenomenon has inspired a good deal of research, much of it coming to similar conclusions.

 

Overnight we saw this press release come from the American College of Chest Physicians.

 

 

'Obesity paradox': Extra weight linked to better outcomes for septic shock, asthma exacerbation

Although obesity is linked to a variety of health risks, new research indicates that obese patients may have an advantage over nonobese patients in certain health situations, including septic shock and acute asthma exacerbation.

 

In two separate studies presented at CHEST 2012, the annual meeting of the American College of Chest Physicians, researchers compared outcomes in obese (BMI >30) vs nonobese patients with either septic shock or acute asthma exacerbation. Results showed that, although obese patients with asthma are more at risk for asthma exacerbations, near fatal exacerbations were more prevalent in nonobese patients.

 

Likewise, obese patients with septic shock had decreased mortality compared with nonobese patients. Researchers attribute this "obesity paradox" partly to a blunted pro-inflammatory cytokine response in obese patients.

 

 

Recently,  JAMA published a pooled analysis of 5 cohort studies that found – surprisingly – that : “Adults who were normal weight at the time of incident diabetes had higher mortality than adults who are overweight or obese.”

Original Contribution | August 8, 2012

Association of Weight Status With Mortality in Adults With Incident Diabetes

Mercedes R. Carnethon, PhD; Peter John D. De Chavez, MS; Mary L. Biggs, PhD; Cora E. Lewis, MD; James S. Pankow, PhD; Alain G. Bertoni, MD, MS; Sherita H. Golden, MD, MS; Kiang Liu, PhD; Kenneth J. Mukamal, MD, MPH; Brenda Campbell-Jenkins, PhD; Alan R. Dyer, PhD

JAMA. 2012;308(6):581-590. doi:10.1001/jama.2012.9282.

 

 

 

We’ve another large study out of Sweden that looked at patient outcomes with acute coronary syndromes (ACSs)  – and you guessed it – obese patients had better survival rates after a heart attack than patients of normal weight.

 

Evidence for obesity paradox in patients with acute coronary syndromes: a report from the Swedish Coronary Angiography and Angioplasty Registry

Oskar Angerås, Per Albertsson, Kristjan Karason, Truls Råmunddal, Göran Matejka, Stefan James, Bo Lagerqvist, Annika Rosengren and Elmir Omerovic

Conclusion In this large and unselected group of patients with ACSs, the relation between BMI and mortality was U-shaped, with the nadir among overweight or obese patients and underweight and normal-weight patients having the highest risk. These data strengthen the concept of the obesity paradox substantially.

 

 

Similarly, from the American Journal of Cardiology, we get this study from earlier this summer, on survival rates of patients with congestive heart failure.

Volume 110, Issue 1 , Pages 77-82, 1 July 2012

The Obesity Paradox in Men Versus Women With Systolic Heart Failure

Adrienne L. Clark, BA, Jennifer Chyu, Tamara B. Horwich, MD, MS

Abstract (excerpt):

In multivariate analyses, normal BMI and normal WC were associated with higher relative risk for the primary outcome in men (BMI 1.34, WC 2.02) and women (BMI 1.38, WC 2.99). In conclusion, in patients with advanced HF, high BMI and WC were associated with improved outcomes in both genders. Further investigation of the interaction between body composition and gender in HF outcomes is warranted.

 

 

Admittedly, many of these medical conditions may well have been brought on by the patient’s obesity to start with, so none of these results should be construed as a green light for binge eating brownies.

 

As to why obese individuals may fare better with certain medical conditions that those of normal, or below normal, weight?  

 

There are plenty of theories.

 

• It has been suggested that heavier patients may develop medical conditions earlier, may get more aggressive treatment, and thereby have a survival advantage.
• Some theorize that hospitalizations and chronic illnesses – which often induce weight loss - put those without fat reserves at a disadvantage.
• There is even speculation that adipose tissue may secrete protective cytokines and hormones (cite).

 

The truth is, no one really knows.

 

Finally, in 2005 epidemiologist Katherine Flegal published a study called Excess deaths associated with underweight, overweight, and obesity that looked at data from two decades of NHANES surveys, and found that mortality among those slightly overweight (BMI 25 -29) was less than those in the `normal’ weight category (BMI 20 -25).

 

This study found that it was really the extremes of being over or underweight that contributed to higher mortality.

 

Personally, I’m not sure what conclusions we can draw from all of this, but it is certainly food for thought.

Of Mice And Menus

 

 

 

# 6336

 

 

I’ve admittedly three reasons for blogging on this non-infectious disease health story this morning.

 

1. I’ve had this blog title in mind for a long time and have been dying for an opportunity to use it.
2. Like many so many others, I’ve been gravitationally challenged most of my life.
3. I’m always fascinated when something new comes along that upends `common knowledge’.

 

Today, a study that appears in the journal Cell Metabolism that calls into question dieting advice of long standing.  

 

• The first is that you should always start your day off with a good breakfast
• The second is that you should eat several smaller meals throughout the day
• And the third is that a calorie is a calorie is a calorie.

 

The study, whose pedigree includes the Salk Institute in La Jolla, is called:

 

 

 

Time-Restricted Feeding without Reducing Caloric Intake Prevents Metabolic Diseases in Mice Fed a High-Fat Diet

Megumi Hatori, Christopher Vollmers, Amir zarrinpar, Luciano DiTacchio, Eric A. Bushong, Shubhroz Gill, Mathias Leblanc, Amandine Chaix, Matthew Joens, James A. J. Fitzpatrick, Mark H. Ellisman, Satchidananda Panda

Summary

While diet-induced obesity has been exclusively attributed to increased caloric intake from fat, animals fed a high-fat diet (HFD) ad libitum (ad lib) eat frequently throughout day and night, disrupting the normal feeding cycle. To test whether obesity and metabolic diseases result from HFD or disruption of metabolic cycles, we subjected mice to either ad lib or time-restricted feeding (tRF) of a HFD for 8 hr per day.

(Continue . . .)

The entire article is behind a pay wall, but we’ve a detailed press release outlining what this study found.

 

Briefly, researchers fed two groups of lab mice the same number of calories each day of high fat food, but in one group only allowed the mice to eat during an 8 hour period. 

 

The other group of mice could nibble round the clock.

 

And the results were astonishing. 

 

While both sets of mice consumed the same number of calories, the ones forced to fast 16 hours each day stayed lean, while the ones who were allowed to `graze’  throughout the day gained a good deal of weight and developed metabolic problems (high cholesterol, high blood sugar, & fatty liver disease).

 

More details via excepts from the press release from the Salk Institute.  Follow the link to read it in its entirety.

 

Salk study may offer drug-free intervention to prevent obesity and diabetes

Extended daily fasting overrides harmful effects of a high-fat diet

May 17, 2012

 

LA JOLLA, CA—It turns out that when we eat may be as important as what we eat. Scientists at the Salk Institute for Biological Studies have found that regular eating times and extending the daily fasting period may override the adverse health effects of a high-fat diet and prevent obesity, diabetes and liver disease in mice.

<SNIP>

Panda's team fed two sets of mice, which shared the same genes, gender and age, a diet comprising 60 percent of its calories from fat (like eating potato chips and ice-cream for all your meals). One group of mice could eat whenever they wanted, consuming half their food at night (mice are primarily nocturnal) and nibbling throughout the rest of the day. The other group was restricted to eating for only eight hours every night; in essence, fasting for about 16 hours a day. Two control groups ate a standard diet comprising about 13 percent of calories from fat under similar conditions.

 

After 100 days, the mice who ate fatty food frequently throughout the day gained weight and developed high cholesterol, high blood glucose, liver damage and diminished motor control, while the mice in the time-restricted feeding group weighed 28 percent less and showed no adverse health effects despite consuming the same amount of calories from the same fatty food. Further, the time-restricted mice outperformed the ad lib eaters and those on a normal diet when given an exercise test.

"This was a surprising result," says Megumi Hatori, a postdoctoral researcher in Panda's laboratory and a first author of the study. "For the last 50 years, we have been told to reduce our calories from fat and to eat smaller meals and snacks throughout the day. We found, however, that fasting time is important. By eating in a time-restricted fashion, you can still resist the damaging effects of a high-fat diet, and we did not find any adverse effects of time-restricted eating when eating healthy food."

(Continue . . .  )

 

 

Of course, experimental results in mice don’t always translate well to humans. So it will take further research to know whether this strategy will prove equally effective in humans.

 

The authors do state that there is reason to hope, as the lead author is quoted as saying:

 

That most successful human lifestyle interventions were first tested in mice, so he and his team are hopeful their findings will follow suit. If following a time-restricted eating schedule can prevent weight gain by 10 to 20 percent, it will be a simple and effective lifestyle intervention to contain the obesity epidemic.

Study: Obesity, Influenza & Immunity

 

 

# 5922

 

 

Even in the earliest days of the 2009 H1N1 `swine’ flu outbreak, it was apparent that most people who contracted this novel virus experienced a relatively mild illness and recovered without incident.

 

There were exceptions, of course. 

 

Some small percentage of people were hit hard by the pandemic H1N1 virus, with some experiencing ARDS (Acute Respiratory Distress Syndrome) and a few sustaining severe lung damage.

 

Thousands died, with most of those deaths occurring in those under the age of 65. 

 

Many (but not all) of them had what was described as underlying `risk factors’; pregnancy, asthma, COPD, neurological disorders, heart failure, etc.

 

Extreme (or morbid) Obesity (BMI > 40) was one of the risk factors that emerged early in the 2009 outbreak, based primarily on anecdotal stories describing many of those admitted to intensive care units during the first wave of the illness. 

 

The earliest mention I can find in this blog of the link to obesity (and smoking) came on May 25th, 2009; scarcely one month after the first swine flu cases were announced in San Diego (see H1N1 Morbidity And Previously Existing Conditions).

 

During 2009 obesity was often mentioned as a possible risk factor (see Obesity Seen As Major Risk Factor For Flu Complications) - then later -  cautiously discounted as unproven (see More On The ACIP Meeting) in late July of 2009.

 

We saw more studies during 2010 that again raised the obesity question, and earlier this year in Extreme Obesity: A Novel Risk Factor For A Novel Flu we saw a study appearing in Clinical Infectious Diseases that found a three-fold increase in mortality among H1N1 patients who were morbidly obese.

 

Given the rising obesity rates in many countries around the world, an underlying risk factor that affects 25%-33% of the population is a pretty big deal.

 

 

All of which serves as prelude to a study that will appear later today in the International Journal of Obesity that looks at the immune response in those who are overweight, and finds significant differences from normal weight individuals.

 

This study found that while overweight people mounted a robust immune response from a flu vaccine during the first month after vaccination, within 12 months half saw a 4-fold decrease in antibody titers. 

 

That’s twice the rate of normal weight individuals.

 

Furthermore, they found significant differences in the immune response of obese subjects that suggest they are not only more susceptible to influenza, but are also more likely to see severe disease or complications.

 

While the study is not yet online, we have the press release from the University of North Carolina School of Medicine. Follow the link to read it in its entirety.

 

 

Study: Obesity limits effectiveness of flu vaccines

Public release date: 25-Oct-2011

 

New research from the University of North Carolina at Chapel Hill shows that obesity may make annual flu shots less effective.

 

The findings, published online Oct. 25, 2011, in he International Journal of Obesity, provide evidence explaining a phenomenon that was noticed for the first time during the 2009 H1N1 flu outbreak: that obesity is associated with an impaired immune response to the influenza vaccination in humans.

 

"These results suggest that overweight and obese people would be more likely than healthy weight people to experience flu illness following exposure to the flu virus," said Melinda Beck, Ph.D., professor and associate chair of nutrition at the UNC Gillings School of Global Public Health and senior author of the study.

 

"Previous studies have indicated the possibility that obesity might impair the human body's ability to fight flu viruses. These new findings seem to give us a reason why obese people were more susceptible to influenza illness during the H1N1 pandemic compared to healthy weight people."

 

The study reports for the first time that influenza vaccine antibody levels decline significantly in obese people compared to healthy weight individuals. What's more, responses of CD8+ T cells (a type of white blood cell that plays a key role in the body's immune system) are defective in heavier people.

 

(Continue . . . )

 

While the authors of this study can observe the decline in antibody response in the obese, the reasons behind it are less clear. They state:

 

"We need to continue to study the effect of obesity on the ability to fight virus infections. Influenza is a serious public health threat, killing up to half a million people a year worldwide. As rates of obesity continue to rise, the number of deaths from the flu could rise too.

 

We need to better understand this problem and to look for solutions."

 

 

Just as we’ve seen with those over 65 (see Study: Flu Vaccines And The Elderly and Flu Shots For The Elderly May Have Limited Benefits), those who are most at risk from influenza often see a reduced benefit from the current vaccine.

 

That isn’t to dismiss the flu vaccine as useless or a waste of time for these higher risk groups. Some protection is undoubtedly better than none.

 

But it is further evidence of the need to develop better flu shots that can help protect everyone.

 

Particularly those who mount a less-than-robust immune response to vaccines today.