what do we know about factors that influence adhd in positiive and negative directions

The evidence on factors that influence ADHD in positive and negative directions is mostly indirect, and the strongest findings are about things to avoid, not things to add.

The clearest negative influence is tobacco smoke exposure. Prenatal and postnatal exposure are linked to worse outcomes across multiple studies. One large Japanese cohort of over 50,000 children found that maternal smoking during pregnancy raised the risk of hearing impairment at age 3 by about 68%, and adding postnatal secondhand smoke nearly doubled that risk [7]. Another study of 470 children found that postnatal smoke exposure was linked to a 24% increase in insulin resistance at age 10 [5]. For infant lung health, postnatal smoke exposure raised the risk of severe bronchiolitis more than fourfold [6]. These are not ADHD-specific outcomes, but they show that smoke exposure harms developing systems that overlap with ADHD risk.

The positive side is much thinner. The gut microbiome is a plausible pathway. Several reviews describe how diet shapes the microbiome and how the microbiome communicates with the brain through the vagus nerve, short-chain fatty acids, and immune signals [2, 3, 4]. High-fiber, nutrient-dense diets support a healthier microbiome, while high-sugar and processed foods are linked to dysbiosis [3]. But these are reviews of animal and correlational human studies. No retrieved trial shows that changing the microbiome improves ADHD symptoms.

Neurofeedback is another candidate. A 2026 RCT of 100 children found that EEG self-regulation during neurofeedback training was real: active participants were about twice as likely to show learning on the theta/beta ratio target as sham controls [1]. But learning did not reliably predict symptom improvement. After correcting for multiple comparisons, no learning parameter remained significant. The only predictor that approached significance was non-specific engagement, not the EEG training itself [1]. This suggests the benefit may come from attention and structure, not from the specific brainwave training.

My call: the strongest actionable factor is avoiding tobacco smoke exposure during pregnancy and early childhood. Diet and microbiome interventions are plausible but unproven for ADHD. Neurofeedback may help some children, but the mechanism is not what is advertised. Confidence: moderate for smoke exposure as a negative factor; low for any positive intervention, because the definitive trials have not been run.