Is there some evidence that humans really react that differently all else being equal? Literally anything that can affect our bodies might be a confounding fac

Is there some evidence that humans really react that differently all else being equal? Literally anything that can affect our bodies might be a confounding factor: sleep; water intake; type, frequency, duration, and difficulty of exercise; sunlight exposure; climate (average temperature, humidity, temperature swings, atmospheric salinity); elevation; latitude, etc...