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Slow Runnings: How much, how often, and how fast should you run?

We often hear of cases in the media describing the deaths of marathoners or other distance runners. Ryan Shay, Jim Fixx, and Pheidippides* are all high profile runners who tragically collapsed and died while running. However, let’s make one thing clear, running is good for you! Since the 1950s studies have confirmed that exercise improves cardiovascular health and decreases your susceptibility of dying during a given period (A.K.A. mortality). So, we know that running is healthy, but how much should we run and how intensely should we run for maximum health benefits? A study published in the Journal of the American College of Cardiology in February 2015 suggests that light and moderate jogging 2-3 times per week is most beneficial in terms of reducing overall mortality when compared to a sedentary lifestyle. Higher-intensity jogging did not show any reductions in mortality compared to sedentary folks.

In terms of aerobic exercise, current Center for Disease Control and Prevention (CDC) guidelines on exercise recommend, “2 hours and 30 minutes (150 minutes) of moderate-intensity aerobic activity (i.e., brisk walking) every week,” or, “1 hour and 15 minutes (75 minutes) of vigorous-intensity aerobic activity (i.e., jogging or running) every week.” Most studies have found that regular exercise reduces mortality compared to sitting on your butt all the time. Some studies have tracked exercisers and non-exercisers over decades and found that physically active people have about a 30% reduction in risk of death during the study period.

The 2015 study by researchers involved with the Copenhagen City Heart Study focused on studying the relationship between the pace, amount, and frequency of jogging and overall mortality. They studied a randomly selected group of healthy joggers (1,098 men and women) and non-joggers (3,950 men and women), all individuals were white in this study group. Anybody in this group with a history of coronary stroke, heart disease, or cancer was excluded from the study. Patients were followed-up from 2001-2013 or until their death, so the period of time studied was about 12 years. Using a survey the researchers assessed the quantity of jogging, frequency of jogging, and a relative perception of running intensity. To assess the influence of running on mortality joggers were split into 3 groups, light joggers, moderate joggers, and strenuous joggers** based on their amount and intensity of jogging or “dose”.  The study analyzed the relationship between quantity of jogging, frequency of jogging, and a relative perception of running intensity and overall mortality using a statistical technique called the Cox proportional hazards regression analysis. Basically, this analysis method examines the treatment effect (quantity, frequency, and intensity of joggin) on survival after adjusting for other potential explanatory values (age, sex, smoking, alcohol consumption, education, and diabetes).

Overall, joggers had fewer deaths (28) than sedentary non-joggers (128). The optimal jogging “dose” for reduced mortality was jogging at a slower or moderate pace for 1 to 2.4 hours per week at a frequency of 2-3 times per week. Out of the light, moderate, and strenuous jogger groups the hazard ratio (mortality risk) was significantly (see central illustration from the paper below) lower than the moderate and strenuous joggers. Strenuous joggers did not have a mortality risk that was any different (statistically speaking) than sedentary individuals. Looking at the figure below, the authors point out that the dose-response curve or running “dose” versus hazard ratio is U-shaped or J-shaped.

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There are a few drawbacks to this study and it doesn’t quite prove that strenuous exercise actually has an equal mortality rate with a sedentary lifestyle. One caveat is that all levels of activity were self-reported and one individual’s perception of strenuous versus non-strenuous exercise is very subjective.  Also, the low, moderate, and strenuous jogger groups seem somewhat arbitrarily define.  Another point is that compared to other treatment groups the strenuous jogger group confidence intervals are quite large and overlap with some of the other treatments, this could be due to a small sample size. However, the study authors state that the strenuous jogging group mortality risk is significantly higher than the light jogger group. This is also a correlative study and can only show associations between running and mortality and cannot prove any causal relationships. So, while the findings of this study are interesting and definitely continue to show that light and moderate exercise is associated with lower mortality rates, it hints at but doesn’t really prove that running at higher paces, mileages, and number of runs per week is dangerous.



*some historians do not believe that Pheidippides, a professional running courier, died after running a marathon to Athens to proclaim a Greek victory over the Persians in the Battle of Marathon. Some believe that the story is a romantic invention, others believe that after reaching Athens he continued on running to Sparta (another 137 miles).



**Light joggers ran 3 times or less each week, for less than 2.5 hours of running each week, and at a slow or average pace of ~5 miles per hour (12 minute mile). Moderate joggers fit several conditions. They ran at slow or average pace (5-7 miles per hour, or between a 12-8:34 minute mile), with 2.5 or more hours of running per week less, and went on 3 or fewer runs per week. Moderate runners were also considered those runners who ran at a fast pace of more than 7 miles per hour (less than an 8:34 mile) for 4 hours or less per week at a frequency of 3 or fewer jogs per week. Additionally, moderate runners were those with a slow or average pace running more than 3 time per week or a fast pace running less than 2.5 hours per week for more than 3 runs per week. Joggers in the strenuous category had a pace of more than 7 miles per hour (less than an 8:34 mile) and greater than 4 hours of jogging per week or alternatively 2.5 hours or more of jogging time more than 3 times per week.

The Organic Effect: Does eating organic reduce pesticide body burdens?

Currently, this video is making its way around social media.

It shows a Swedish family that switches from eating conventionally produced food to an all-organic diet. The video claims that pesticide residues in the urine of each of the family members were reduced after 2 weeks of the organic food diet. While I am all for healthy eating and think organic food is great, I was a little skeptical of the ideas that were being pushed in this short clip. Do pesticides residues actually drop that quickly when switching to organic food? Also, it was funded by Coop Sverige AB, a large Swedish supermarket and retail chain, that may have some vested interest in the outcomes of this research. The research group that actually carried out the testing and reporting is the IVL Swedish Environmental Research Institute. According to their website they are an “independent, non-profit research institute, owned by a foundation jointly established by the Swedish Government and Swedish Industry. I am not familiar with this research group, but one would hope that they are unbiased. The viral video is pretty vague, but a more detailed report is freely available, so I delved a little further to see what it had to say.

The researchers sampled urine from a family of 4 for a three-week period. The first week was a continuation of their normal diet that did not include much organically produced food. During the second week they switched to an all-organic diet. The twelve pesticides measured are shown in the table below.

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* indicates that a metabolite of the original compound was actually measured in urine

During the non-organic diet phase of this experiment 8/12 analyzed pesticides were detected in at least one urine samples at median concentrations shown in the figure below. Note that concentrations of these pesticides in urine were still well below levels deemed safe (See Figure 1).  Pesticide residues are reported as μg/g creatinine as they are standardized to creatinine levels in urine to standardize for different levels of hydration in individuals at different times.

After the period of consuming only all organic food only 5/12 pesticides were detected in each urine sample and they were found at much lower levels (See Figure 1).

Figure 1: Concentrations of pesticides in urine before and after an organic diet in a family of 4



The study is fairly well documented although it would be good to see the methods critiqued and go through the peer review process. However, the science seems pretty sound. The sample size of only 4 individuals in one family is fairly small.  Overall, the results make sense in that if you reduce exposure to synthetic pesticides by consuming organic foods your body burdens of those chemicals should decrease over time. The amazing thing to me is that this was detectable after just a two-week switch to organic foods.

Does it matter?

I think it is great if we can reduce the amounts of pesticides we use and our exposures to them. However, remember that even before switching to the organic diet pesticides residues were well below acceptable levels. Also, organic foods do contain “natural” non-synthetic pesticide residues. A 2012 Scientific American article by Christie Wilcox summarizes the scientific evidence on whether reducing pesticide loads by eating organic foods has health benefits compared to consuming conventionally produced foods and concludes that it does not. However, we still have little idea how these individual chemicals act in complex mixtures within our bodies.