I wrote back in January about the large numbers of studies that are publicized in the media that doctors and patients are better off ignoring.  I usually try not to give these studies any attention, but this week a study got so much media coverage that I felt I had to tell you all to ignore it.

This study in the journal Circulation looked at participants in the Framingham Heart Study (a large study of heart disease risk factors that started in the 1940s) and looked to see if a link existed between soft drink consumption and the metabolic syndrome.  The metabolic syndrome is a collection of factors (abdominal obesity, elevated blood glucose, elevated blood pressure, elevated triglycerides, and low HDL) that increase the risk of developing diabetes and heart disease.  The study found that those who drank soft drinks were at higher risk of developing the metabolic syndrome than those who didn’t, even if those drinks were diet (non-caloric artificially sweetened) drinks.  This apparently surprising finding generated much media coverage including this article in the Washington Post.

The problem with this study is the same as the problem with all the studies we should ignore.  It was an observational study, not an experiment.  (Check out my January 5 post if you need a refresher on the difference between observational studies and experiments.)  The study didn’t tell some people to drink soft drinks and some people to drink tap water.  It simply observed what they were already doing.  So the study can’t suggest that soda drinking causes the metabolic syndrome, just that the two things tend to happen in the same people.

There is no likely mechanism through which diet sodas can cause the metabolic syndrome.  What is much more likely is that people who tend to be heavier tend to like drinking sweet drinks, so they drink more soft drinks (both diet and regular) than skinny people.  So soda drinking almost certainly doesn’t cause metabolic syndrome.  A drive to consume sweets is likely behind both soda drinking and the metabolic syndrome.  So please, ignore this study.

I’m grateful to my patients Luetrell T. and David D. for sending me links to articles about this study.

The Cochrane Reviews are systematic rigorous reviews of the medical literature on medical therapies.  Because of the objective and comprehensive methods they use for finding all relevant studies and categorizing them by quality, they are regarded as one of the gospels of evidence based medicine.

Recently the Cochrane Reviews published this review of the medical literature on vitamin C for the prevention and treatment of colds.  The study was publicized in this WebMD article.  The results are summarized below.

In studies on the general population, taking vitamin C daily year-round did not prevent getting colds but reduced the duration of colds slightly (8% duration reduction in adults, 14% in children).  The exception was in studies done under extreme low temperature or extreme physical stress, for example studies on marathon runners, skiers, and soldiers in sub-arctic conditions.  In these extreme conditions, daily vitamin C decreased the incidence of colds by about 50%.

In studies that looked at taking vitamin C only once a cold has started, there were no significant differences between vitamin C and placebo.

So, if you take vitamin C only once you’ve caught a cold, you might as well not.  To have any benefit, you have to take it preventively every single day, and for that effort you only get an 8% reduction in the duration of a cold.  This amounts to a 7 day cold being only 13 hours shorter.  For most people, that’s not really worth it.  On the other hand, the authors suggest that if you will be engaging in very strenuous physical activity or exposed to very cold temperatures, daily vitamin C is worth the trouble.

Tangential Miscellany:

Thanks to David W. for pointing out this letter in the New England Journal of Medicine which documents a rare danger of using earphones outside during a thunderstorm.  Ouch!  There’s no mention of what music he was listening to.  I hope it was something great.

This week another dietary supplement moves from the “not proven to have any benefits” column to the “potentially harmful” column.  A study in the Annals of Internal Medicine which was reported in this CNN article is the largest study yet to look at the effects of selenium on the development of diabetes.

This story actually starts over a decade ago with a study designed to test if selenium prevents cancer.  The authors randomized 1,312 patients of a dermatology clinic with a history of skin cancer to receive either a selenium supplement or placebo.  The patients were then followed to see if selenium led to a lower risk of developing new skin cancers.  It didn’t.  (The results were published in this 1996 paper in the Journal of the AMA.)

In this week’s study the data from the first study was re-analyzed looking at the development of diabetes.  Patients who had a diagnosis of diabetes at the start of the study were excluded, and numbers of patients in each group who developed diabetes during the initial trial were counted.  Surprisingly, the patients in the selenium group developed diabetes more frequently than the placebo group at a rate that suggested that for every 25 people who take selenium rather than placebo for 10 years one additional case of diabetes would result.

So selenium doesn’t prevent skin cancer and may actually increase the risk of developing diabetes.  Of course we already have lots of ways to increase the risk of diabetes.  My favorite one is cheesecake.

Thanks to Linda T. for pointing me to this story.

This week’s New England Journal of Medicine published a study funded by Boeing which has received much media attention, including this Washington Post article.

The study sought to reveal the effects on passengers of different cabin pressures during prolonged flights.  The authors hoped to find whether different pressures made passengers uncomfortable or caused acute mountain sickness, an illness marked by headache, shortness of breath and nausea which is caused by rapid altitude gain.  Typically airplane cabins are pressurized to a pressure equivalent to an altitude of 8,000 feet, since maintaining normal atmospheric pressure during a flight would require much more fuel and would increase wear on the airframe.

The study placed volunteers in a hypobaric chamber to simulate a 20 hour flight.  Simulated flights were conducted with the chamber pressurized to different altitudes and the patients were monitored for adverse events.  They also completed a questionnaire about their symptoms.  For the sake of realism, I hope they underwent a prolonged and detailed security screening and had their deodorant summarily confiscated.

The good news is that no one developed acute mountain sickness.  Passenger discomfort, however, increased with decreasing pressure.  There was less discomfort when the cabin was pressurized at 6,000 feet than 8,000 feet.  Since Boeing sponsored this study, I assume they’re about to announce sales of an airframe that remains pressurized to 6,000 feet, heralding a new era of travel comfort.

At least now I know why I was uncomfortable during our family’s recent flight to Orlando.  Until this week I thought it was because the food was horrible and my three year-old wouldn’t stop hitting me.