A Harvard University study concluded that a constant, relatively low-level exposure to common pesticides found on fruits and vegetables doubles children’s risk of developing attention deficit hyperactivity disorder.

Over 1,100 kids aged 8 to 15 participated in the study, which revealed that kids with higher levels of organophosphate were twice as likely to have ADHD as kids with undetectable levels of organophosphate.

Fruits and vegetables high in pesticides include strawberries, peaches, apples, blueberries, celery, bell peppers, spinach, and kale – fruits and vegetables we usually eat without peeling. Fruits and vegetables that require less pesticides include onions, avocados, pineapples, kiwis, and sweet potatoes, and these are fruits and vegetables we normally eat without the skin anyway.

What to do? Buy organic whenever you can – at least of those fruits and vegetables that have higher levels of pesticides.