This pilot aimed to examine the initial status of selected molecular biomarkers involved in metabolic networks that may impact the brain response to head injury in a group of elite American football athletes preparing for the NFL draft. The purpose was to understand the extent of essential micronutrient deficits, along with abnormal surrogate markers, such as Hcy and blood lipids. This design helped us explore the likelihood of an athlete having a nutrition or metabolic abnormality while entering the contact environment. Similarly, this study helps lay the groundwork for a precision nutrition approach to athletes in training. Beyond nutrient effects on performance and recovery, the analytes in this study can be viewed in the context of anatomical structure, biological function, and with attention to how their status may affect the trajectory of an acceleration injury to the brain, potentially providing new insights into concussion prevention and management.
The most compelling results are the frequency distribution of undesirable values found in this cohort. Using the optimal performance ranges, there were no athletes with fewer than two abnormalities in blood values. Significantly, 10% of athletes had 3 undesirable values, 40% had 4 undesirable values, and 50% had 5 undesirable values. This suggests multiple abnormal values important to metabolic networks can be found in small cohorts of elite athletes. Considering the role of related molecular networks in brain metabolism and the potentially nonlinear converging impact of multiple abnormalities [22], this argues the case for prophylactic molecular profiling of individual athletes. It is time to consider the roles of these molecules in brain metabolism and in clinical outcomes associated with brain acceleration injury.
These athletes presented with a suboptimal O3 Index after their collegiate season. A study of German elite athletes revealed an O3 Index comparable to our cohort (4.97 ± 1.19% versus 4.66 ± 1.16%, respectively) [19]. Lewis et al. compared DHA levels in 800 active military suicide deaths to 800 controls. Suicide risk was 14% higher per std of lower DHA percentage (OR = 1.14; 95% CI, 1.02–1.27; p < 0.03). Among men, risk of suicide death was 62% greater with low serum DHA status (adjusted OR = 1.62; 95% CI, 1.12–2.34) [9].
In our cohort, the mean AA:EPA ratio of 29.13 was substantially higher than that of average American males (16.2) and the optimum level (< 5.1) [20]. Linoleic acid contributes to the AA:EPA ratio and omega-6:omega-3 ratio. An a priori paired samples T-test of our data found linoleic acid was significantly lower in athletes who were drafted versus those who were not drafted (p ≤ 0.05). In a study of 170 adults, linoleic acid and arachidonic acid were two of six metabolites that could be used to differentiate between TBI patients with and without cognitive impairment [23].
Homocysteine (Hcy) is an intermediate formed during methionine to cysteine metabolism and is directly dependent upon one-carbon metabolism (B12, folate, betaine, choline). Previous studies have shown excessive Hcy causes vascular endothelium injury, facilitates smooth muscle cell proliferation, accumulates in the blood, and increases the risk of venous thrombosis [24]. Also, elevated Hcy is associated with brain atrophy, silent brain infarcts, and white matter hyperintensity. Such brain vascular changes may have particular relevance to athletes competing in concussion-prone sports.
In a study examining the changes in methionine/homocysteine network, severe TBI decreased methionine, SAM, betaine and 2-methylglycine, as compared to healthy volunteers. Mild TBI also decreased methionine, α-ketobutyrate, 2-hydroxybutyrate, and glycine, though to a lesser degree than the severe TBI group. Of particular interest was a decrease in betaine, a direct methyl donor to Hcy and crucial in the removal of excess Hcy. This further suggests that Hcy may be implicated in TBI outcomes [25].
In our cohort, 90% showed elevated Hcy (11.4 ± 3.4, range 8.2–27.2), which is in accordance with other studies [12]. Elevated Hcy is frequently associated with low B12 or folate. In our cohort, vitamin B12 and folate were clinically normal, which suggests other potential Hcy influencers. VitD binds and activates the vitD receptor, regulating cystathionine-β-synthase transcription and facilitating the conversion of Hcy to cystathionine [26]. While this relationship is known, vitD and Hcy were not correlated (r= -0.167, p = 0.376) in our cohort. Larger studies are needed to understand the full extent to which vitD influences Hcy levels in athletes.
There is little published data on vitD and TBI. However, a study of 353 adults (26.6–48.3 years) seen 0.3–56.5 months after moderate to severe TBI is informative. TBI adults with vitD deficiency had significantly lower Addenbrooke's Cognitive Examination scores, compared to those who were vitD insufficient and replete (p = 0.003 and p = 0.034 respectively). VitD deficiency was also associated with more severe depressive symptoms [27].
VitD influences athletic performance through hundreds of processes, including exercise-induced inflammation, neurological function, cardiovascular health, glucose metabolism, bone health, and skeletal muscle performance including strength and power. In our cohort, 66% of athletes just left a school above the 37th parallel in the United States where it was the winter season, and time spent outside was likely with full gear or clothing. 97% of this study’s athletes had vitD levels lower than suggested minimum for optimal athletic performance (50 ng/mL) and minimal risk for CVD (60 ng/mL) [16].
Neuronal Mg concentrations are of central importance in the regulation of N-methyl-d-aspartate (NMDA) receptor excitability. NMDA receptors are essential for neuronal plasticity, excitatory synaptic transmission, and excitotoxicity, therefore playing an important role in developmental plasticity, learning, and memory [17]. Mg in the brain is seen as crucial to function, though its role in concussion is not definitive. Research has explored the effect of Mg status pre-injury [28] and the effect of Mg post-injury [29] with equivocal results. However, Mg treatments have significantly delayed ischemic infarction [30]. In our cohort, Mg depletion may result from inadequate intake, or following intense exercise, stress, or sweating when low plasma volume causes a cellular shift.
Research has proposed essential and conditionally essential micronutrient deficits (or excess) aggregate and spread across molecular networks. An abnormality can have a broad impact on normal function and on response to trauma, and more than one concurring can amplify across molecular networks in ways that may not be linear [22].
There are several limitations with this study including small sample size, absence of a control group, and no intervention phase, but this study design was observational. Also, we examined a smaller pool of (targeted) analytes in this pilot, which limited our ability to more broadly survey molecular pathways and networks for additional physiological risk to these athletes.