Do epidemiological data on exercise and substance abuse support prescriptions for prevention?

A Twitt from the Foundation for Alcohol Research (@AlcoholResearch) today struck my attention. It sounded to me like the usual slippery slope of creating human health prescriptions from limited scientific findings.

Teen athletes may drink more, but smoke less & use fewer drugs. How do you lessen your teen’s risk? http://bit.ly/mysWna

The link is to their newsletter which overviews a paper by Terry-McElrath and O’Malley, currently in pre-print at Addiction. The overview is pretty straightforward, based closely on the paper and eschews the problem with the Twitt, which was the question as to whether you could “lessen your teen’s risk”. So I am mostly mollified.
The paper in question reports data from a survey of over 11,000 US high school seniors (classes of 1986-2001), captured as seniors and then followed longitudinally until age 26. These data were collected as part of the Monitoring the Future study which we discuss quite frequently on this blog.
The key focus of this paper is on the amount of physical activity the surveyed HS seniors reported at first contact. The Participation in Sports, Athletics or Exercising (PSAE) measure was derived:

…by asking, “How often do you actively participate in sports, athletics or exercising” (1=never, 2=a few times a year, 3=once or twice a month, 4=at least once a week, 5=almost every day).

The other questions of interest to this analysis were the ones relating to past-30-day use of various recreational drugs. This is a part of the MtF dataset that we have discussed now and again. I like it better than the past-12-month and Lifetime measures because it gets us away from the population who has just sampled a drug once or twice and biases it more for those who use the substance occasionally-to-often, for lack of a better concept.
The drug analysis used frequency of use for marijuana/cannabis, alcohol and tobacco smoking. Other illicit drugs other than marijuana were combined into a single dichotomous variable because they occur at a much lower frequency.
There is a lot of correlational statistical foofraw involved in something like this, I’ll omit the details for this purpose. At the end of the selected study window (with the sample aged 26 with 4 followup surveys attempted), the authors ended up with a sample of 40,424 individuals.
The key results were that
-alcohol use at 18 was positively associated with PSAE (see below for a clue as to why)
-rate of change in alcohol and PSAE from 18-22 did not co-vary, there was a positive relationship from 22-26 years of age.
-increasing PSAE values from 18 to 25 were associated with decreased cigarette use.
-increasing PSAE values from 18-22 were associated with decreased marijuana and illicit drugs other than marijuana but there was no relationship from 22 to 26.
Another paper from this group took a related focus and provides some additional valuable context. Terry-McElrath, O’Malley and Johnston examined PSAE and drug use just within the middle- to high-school population (8th, 10th, 12th grades). It doesn’t get at the question of lasting impact but it is perhaps more relevant to the question of acute intervention during the teen years and what can/cannot be accomplished. These analyses took into account participation in school-centered athletics separately from a more global estimation of exercise/physical activity and found that the frequency of exercise was related to decreased past-30-day and binge alcohol use in high school. In contrast, increasing athletic team participation was associated with increased alcohol use. A similar relationship held for smokeless tobacco use. The exercise and athletic team participation frequency measures were both negatively associated with tobacco and marijuana smoking.
This latter paper really brings to a fine point the prescriptive query in the motivating Twitt. If you push your teen onto a sports team, these data suggest that s/he will be more likely to drink alcohol and use smokeless tobacco products. If you push your kid into less team oriented endeavors, the more they work out, the less likely they are to use cigarettes, marijuana or alcohol.
That’s the best read. But of course we know, in the back of our minds, that these are just correlations in both of these papers. There are a whole host of factors which influence sports / team / exercise participation in high school and then additional ones as one grows into young adult hood. There are other factors which may influence how seriously a given teen takes their participation in team sports, which team sport they select and how much exercise it requires, etc. For all we know, there is nothing there in the nature of a direct neurobiological connection between increased activity and decreased drug use/liking whatsoever.
Perhaps the factors which cause your kid to work out also cause her to disdain drugs? [personal anecdote: two major factors kept me from ever trying marijuana in adolescence- one of which was my assumption that the smoking part would be detrimental to my performance in the aerobic sporting endeavors that was in to at the time.]
This brings me to two additional papers which have the benefit of removing the social and other extraneous factors. In a paper that was reviewed by Scicurious at Neurotic Physiology awhile ago, Cosgrove and colleagues gave rats access to a running wheel until they were “stable” (not specified). They next permitted the rats to self-administer cocaine. The key manipulation was when they presented the rats with the simultaneous opportunity to respond for drug or run on the wheel. The amount of cocaine taken dropped significantly (in females, similar but nonsignificant outcome in males). Almost there. Smith and colleagues nailed it down even better. They allowed female rats access to a running wheel for 6 weeks and then trained them to self-administer cocaine. This was a between-groups study (unlike Cosgrove et al) and they showed that the exercised rats took less cocaine (two different per-infusion doses under a Progressive Ratio schedule) than did the sedentary rats.
These, in combination with the epidemiological data, are the start of something. Together they start to get us closer to something like an ability to make a prescriptive decision that if we make our teens exercise more we may have an impact on their propensity to use recreational drugs.
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Terry-McElrath YM, & O’Malley PM (2011). Substance Use and Exercise Participation Among Young Adults: Parallel Trajectories in a National Cohort-Sequential Study. Addiction (Abingdon, England) PMID: 21561496
also see
Terry-McElrath YM, O’Malley PM, & Johnston LD (2011). Exercise and substance use among American youth, 1991-2009. American journal of preventive medicine, 40 (5), 530-40 PMID: 21496752