Plasma BDNF Differed by Sex and Sport Contact Level in 120 Teen Athletes

A new cross-sectional study of 120 uninjured teenage athletes found that plasma BDNF, a blood protein being tested as a concussion marker, tracked with sex, age and the contact demands of the sport played. It did not track with how many concussions an athlete had already had.

Plasma BDNF lined up with who an adolescent athlete was more than with what had happened to them, according to a cross-sectional study published on 2 November 2026 in Scientific Reports. The analysis, nested inside a multi-site Canadian cohort study, measured the protein in 120 adolescent sport participants who were uninjured at the time of testing.

The sample was split evenly by sex. Sixty male participants had a mean age of 15.79 years, with a standard deviation of 1.17, and sixty female participants had a mean age of 15.97 years, with a standard deviation of 1.36. None had an active injury when blood was drawn, so the readings describe a baseline rather than a reaction to a blow to the head.

The clearest signal was a sex difference. Plasma BDNF was significantly higher in males, with a reported coefficient of 0.176 and a 95% confidence interval of 0.010 to 0.342 at p = 0.038. Age was also linked to plasma BDNF, but only in the female participants, where the coefficient was 0.089 with an interval of 0.002 to 0.176 at p = 0.044.

The association that did not appear is the one that matters most for the protein’s proposed clinical use. Concussion history showed no statistically significant relationship with plasma BDNF, with a coefficient of -0.149, an interval of -0.323 to 0.025, and p = 0.093.

What the Study Measured in 120 Adolescent Athletes

The work sits inside a larger Canadian research programme on youth sport injury, and the authors acknowledge funding tied to the SHRed Concussions study. Participants were grouped by the contact demands of their sport, using three categories named in the paper: non-contact, contact and collision. Blood samples supplied the plasma BDNF values that the regression models then tried to explain.

Alongside sex, age and sport category, the models took in height, bodyweight, body mass index, concussion history and, for female participants, menstrual cycle phase. The aim was not to diagnose anyone. It was to find out which ordinary characteristics move plasma BDNF before any injury enters the picture.

Sex and Age Explained More Than Concussion History Did

Reading the published estimates side by side, the ranking is hard to miss. Sex, age in females and sport category all reached conventional statistical significance. Concussion history, the one variable a plasma BDNF concussion test would have to be sensitive to, did not.

That pattern echoes a theme running through recent work on exercise and the bloodstream, where biological noise can swamp the signal a researcher is hunting for. An earlier analysis covered by this magazine found that exercise shifted more than 3,000 proteins in a single human study, which gives a sense of how crowded that measurement space is.

Contact Sport Participation Tracked With Lower Plasma BDNF

Participants whose sport involved contact had significantly lower plasma BDNF than those in non-contact sports. The paper reports that difference as -0.462, with an interval of -0.830 to -0.093, at p = 0.014. Since nobody in the sample was injured, the authors treat this as a feature of the athletes and their sport rather than evidence of damage.

Why contact athletes would sit lower on plasma BDNF at baseline is not settled by a cross-sectional design. Training history, body composition, sport selection and the sheer variety of activities folded into one category are all candidates, and none can be separated out here.

Height Moved With the Protein, but Weight and Body Mass Index Did Not

Height was reported as positively associated, at 0.011, with an interval of -0.001 to 0.021 and p = 0.028. Readers should note that the interval as published spans zero, which sits awkwardly beside a p-value under 0.05 and is worth watching in the final version of record.

Bodyweight and body mass index did not clear the usual threshold. Bodyweight came in at 0.005, with an interval of -0.001 to 0.012 at p = 0.119, and body mass index at 0.006, with an interval of -0.017 to 0.029 at p = 0.062. Body size, in other words, matters in some form, but the simplest measures of it did not carry the signal.

Menstrual Cycle Phase Showed No Significant Link to Plasma BDNF

Among female participants, menstrual cycle phase was not significantly associated with plasma BDNF, at -0.210, with an interval of -0.470 to 0.051 and p = 0.114. The estimate points downward but the interval is wide, which is what a sample of sixty females tends to produce. Cycle phase was measured because it is a plausible influence on plasma BDNF, and the paper reports the result rather than assuming one.

Cycle phase has become a standard covariate in female athlete research for good reason. Earlier FLM coverage of brain blood flow responses to resistance exercise that did not differ by sex is a reminder that expected sex differences do not always appear, and that both results are useful.

Why Plasma BDNF Is Being Studied in Sport at All

The authors open by noting that brain-derived neurotrophic factor is being explored as a biomarker for sport-related concussion. The appeal is obvious. A blood test that flagged an injury objectively would reduce the guesswork in sideline decisions about young athletes, where the current judgement call often has to be made in minutes, by people who are not clinicians, on a field with no equipment beyond a checklist and a stopwatch.

This study does not test that use. It asks a narrower and prior question: what does the protein look like in healthy adolescent athletes, and what moves it. The answer the paper gives is that several routine characteristics move plasma BDNF, which complicates any attempt to read a single value as normal or abnormal.

Youth sport is a large and growing setting for that question. FLM has reported that organized youth sport participation rose from 50.4% to 63.4% across a decade in 5,027 Slovenian teenagers, and that physical fitness was linked to better arithmetic fluency in 1,166 adolescents.

What This Does and Does Not Mean for Young Athletes

Nothing in this study changes how a suspected concussion should be handled. There is no blood test here to ask a clinician for, and no reading a parent or coach can act on. What the paper offers is a caution about interpretation: a single plasma BDNF value, taken out of context, would be difficult to judge.

For families following concussion research, a few points hold up:

• Plasma BDNF research of this kind is still establishing what a normal reading looks like, which comes well before any clinical use.
• Sex, age and the type of sport played appear to shift plasma BDNF in uninjured athletes, so comparisons need to be like for like.
• Concussion recognition and management still rest on symptoms, clinical assessment and graded return to activity, not on a blood draw.
• Any concern about a head injury in a young athlete is a question for a qualified clinician, not for a research summary.

Injury surveillance gives useful context for how often these decisions come up. An FLM review of national data found that exercise-related injuries reached an estimated 5.49 million over 12 years in the United States, a scale that explains the appetite for objective tests.