What the Flip is BDNF?
Workshopping an Age-Old Adage
Image: BDNF at Work on Skynet [my title]
I’m taking a course this semester (Exercise Science, baby!1), and the topic of BDNF came up. There are some very cool things that this little molecule does, and there are some things we can do in order to promote its production and uptake in the body, so I’m writing this article in order to, one, sort of study and bone up on it all, and, two, to share some of these details.
In the nerdier corners of the healthspace, BDNF comes up now and again, but it can get a little complicated pretty quickly. Still, despite its complexity, the fact that it’s making its way into these and even other, more popular spaces, shows, if anything, there’s something going on here.
BDNF is Brain-Derived Neurotrophic Factor, which, if you’re like me and come largely from a liberal arts background, might as well be baby babble, without sounding quite as cute. Still, I think I can process this into simple enough terms that even I can understand and explain it.
So, a neurotrophic factor is a type of protein called a neurotrophin, which “regulate[s] development, maintenance, and function of vertebrate nervous systems.” More specifically, “These proteins also regulate many aspects of neural function. In the mature nervous system, they control synaptic function and synaptic plasticity, while continuing to modulate neuronal survival.”2
All of that’s to say that neurotrophins are responsible for maintaining the health, well-being, and consequently, the longevity, of neurons—you know, nerve cells. Neurotrophins like BDNF also work to preserve and maintain brain cells, so they essentially work to keep our brains healthy, thereby maintaining our cognitive function and our memory.
Like everything else, as we age, the biological good stuff gets a little harder to come by—a little harder but not impossible. “In humans, circulating levels of BDNF decline with advancing age… [and] Lower levels of BDNF were associated with smaller hippocampi and poorer memory.”3 No bueno.
The goal of anyone who lifts weights is to get, as they say, as jacked as possible. Most of us I think would also like to buff up and hopefully maintain that all-important muscle between our ears.
It seems like BDNF might be one way to do just that. If only there was some way we might be able to somehow promote its production.
AH, but it looks like there are some ways.
The first is aerobic exercise. Either acute (a single session) or chronic (long-term training) aerobic exercise activity will result in an elevation of blood BDNF levels; it’s transient but still very observable and very significant.
In one systematic review of studies on exercise-induced BDNF levels, the authors found that “Sixty-nine percent of the studies in healthy subjects and 86% of the studies in persons with a chronic disease or disability, found a ‘mostly transient’ increase in peripheral BDNF (ranging from 11.7% to 410.0%) following an acute exercise protocol, with the tendency of acute high-intensity exercise protocols and GXTs [graded exercise tests] having larger increases in BDNF concentrations than acute low-intensity exercise protocols.”4
A few things of import here. This transient increase lasted for only a short period, with levels returning to baseline within 60 minutes, but the authors note that BDNF concentrations return to baseline so quickly because these extra proteins are rapidly absorbed into the body’s tissues, where they will go about their maintenance and repair work.
Also, intensity seems to be more beneficial, resulting in higher BDNF production. So, walking, typically a low-intensity activity, will still elicit some extra BDNF, but something more rigorous for you (scale the work to your fitness levels) will result in even greater BDNF levels.
Moreover, I was kind of blown away to learn that individuals with chronic diseases and disabilities can also significantly raise BDNF levels, and a cool thing is that they seem to do just as well with doing so through lower-intensity work compared to healthier folks and higher-intensity work. There have already been studies with people who have MS and spinal cord injuries, and they can promote higher levels of BDNF in the same way.
So, how does resistance training fare with BDNF?
Some studies show that resistance training increases circulating BDNF concentrations while other studies show no increase. However, there are a couple of points that may explain the difference in outcomes. The studies that tend not to show an increase are with untrained subjects, most often college students who don’t regularly lift weights. At first, these subjects don’t tend to show increased BDNF levels, but after five weeks of consistent training, they do.
Some other studies that show no increase in BDNF from resistance training tend to have protocols that are considered low intensity, that is, working much farther away from the participants’ absolute strength capabilities. The studies that show BDNF increases are the ones that use higher-intensity protocols; that is, the subjects work with higher loads, closer to their one-repetition maximal strength capabilities. In the previously cited systematic review, the authors note that “A dose-response relationship exists between the intensity of the exercise and peripheral BDNF concentration… [and] Presumably, an acute strength exercise stimulates peripheral BDNF on the condition that the exercise load is intensive enough.”
It appears that aerobic exercise definitely elicits BDNF production, either low or high-intensity, and it appears that resistance training will also increase BDNF levels on the conditions that we are lifting heavy enough and/or that we have been doing it consistently for at least a few weeks.
We know we can increase our circulating BDNF levels acutely after exercise. So what? What does all that mean?
On the brain side of things, “With accumulated bouts of exercise, the repeated exposures to doses of BDNF would be expected to elicit functional and structural adaptations in the brain” and “exercise can help to maximize an individual’s exposure to acute doses of BDNF over the course of an exercise intervention and potentially maximize brain plasticity.”5 And as the titles of these studies put it: “Exercise training increases size of hippocampus and improves memory”6 and “Exercise builds brain health”.7 We’re essentially talking about protection against neurodegeneration.
On the body’s side, aerobic exercise and resistance training maintain those motor networks, even independent of BDNF, but it appears that BDNF will provide increased upkeep of those pathways.
Some other points to consider, which haven’t been the focus of these studies but has still been mentioned in the periphery are other factors that affect BDNF levels, such as nutrition, metabolic conditions, and even emotional states.
Diets that are inadequate or insufficient for nutrients often show lower levels of BDNF concentrations, which can also be the case when considering energy availability. For those of us who go into deficits a couple of times a year, periods of energy restriction will also decrease BDNF levels. Metabolic conditions, like diabetes, hypertension, even heart disease, also show lower BDNF concentrations. Interestingly, depression can affect the levels of BDNF, which can be mitigated with exercise.8
What are the practical takeaways and the actionable steps here?
First, I don’t think any of us should think about brain-derived neurotrophic factor as some sort of panacea or magic bullet, but I think it reaffirms what most of us already know and intuit: movement and exercise is good. If we frequently exercise, we are frequently elevating BDNF levels in our bodies, those molecular proteins that repair and maintain nerve cells and brain cells; logically, this elevation should result in less natural decaying of these cells and pathways, thereby helping us remain active, more physically and cognitively robust, and for longer.
The more frequently we exercise, the more frequently we are producing, releasing, distributing, and absorbing this potent protein. If we’re sedentary and being lax with nutrition, not to mention not controlling stress, poor sleep, mental wellbeing, indulging in other fill-in-the-blank unhealthy behaviors, we’re probably going against the grain and downregulating BDNF and other important health promoting molecules.
Second, especially for those of us who lean more towards weights, it’s a friendly reminder how beneficial aerobic exercise is. Even adding a couple of walks a week might be a good start. If you’re already doing some form of cardiovascular exercise, you might consider having at least a weekly session that is a higher-intensity, which means working harder but also for less time. (You can’t sprint for 30 minutes.)
If you’re a low-intensity-steady-stater (like walking) or an endurance athlete, you might consider throwing a couple of sprints into your regimen once a week, as a start. (The sprints can be of any modality—cycling or rowing, for example—it doesn’t have to be running. And, again, scale the work to your levels.)
For the monogamous cardiophiles out there, it’s also a friendly reminder to move those Muskols regularly, but, like cardio, we want to have bouts of higher-intensity work—that is, higher loads, fewer reps—closer to maximal effort with shorter bouts.
We can’t build an exercise or training program with all high-intensity work. Well, we can certainly try, but it’s not sustainable, and my whole thesis for The Flexitorium is designing menus and food plans and exercise routines that work for you, that are health-promoting, and that are sustainable.
Periods, sessions, and bouts of high-intensity work, in my opinion, is absolutely necessary, but we will grind ourselves into the ground if we try to cruise at top speed all of the time, which is exactly what I would do all throughout my teens and early 20s. We want to thoughtfully and strategically place high-intensity work in the most logical places because this is the work that results in the most fatigue and thus requires the most recovery time. And if we’re planning a period of a higher volume of high-intensity work, we need to remember that it’s a finite period and shouldn’t be open-ended or go on indefinitely, which gets into the tenets of training periodization—blocks of work of different intensities.
This is a parallel to energy manipulation, too. The more you deviate from your maintenance energy levels, above or below, the less time you should spend there.
Overall, it looks like the evidence on BDNF is confirming the age-old adage of “Use it, or lose it,” but it also shows a new one that we should all remember: “Use it, and build it.”
Shout out to Dr. Zourdos, who has no idea I’ve written this but whose class materials have inspired it.
Kirk I. Erickson, Ruchika Shaurya Prakash, Michelle W. Voss, Laura Chaddock, Susie Heo, Molly McLaren, Brandt D. Pence, Stephen A. Martin, Victoria J. Vieira, Jeffrey A. Woods, Edward McAuley, Arthur F. Kramer. “Brain-Derived Neurotrophic Factor Is Associated with Age-Related Decline in Hippocampal Volume.” Journal of Neuroscience. 14 April 2010, 30 (15) 5368-5375; DOI: 10.1523/JNEUROSCI.6251-09.2010
Erickson KI, Voss MW, Prakash RS, Basak C, Szabo A, Chaddock L, Kim JS, Heo S, Alves H, White SM, Wojcicki TR, Mailey E, Vieira VJ, Martin SA, Pence BD, Woods JA, McAuley E, Kramer AF. “Exercise training increases size of hippocampus and improves memory.” Proc Natl Acad Sci U S A. 2011 Feb 15;108(7):3017-22. doi: 10.1073/pnas.1015950108. Epub 2011 Jan 31. PMID: 21282661; PMCID: PMC3041121.