Chromium is important for lowering insulin levels. Excess iron has been implicated in heart disease and other conditions. Heat dramatically lowers serotonin levels because serotonin is used up trying to cool down the body. That's why everyone gets so cranky when they're hot. People with low serotonin levels have trouble sweating and staying cool.
Regular exercise increases both serotonin and dopamine, and affects other important systems as well.
The role of exercise for both physical and mental health has been well established. Buy an air ionizer. Yes, it sounds weird, but air with negatively charged particles appears to help out serotonin in the brain. Pollution and the modern world have nearly eliminated naturally charged air in urban areas. You can feel the pleasant effect of negative ions whereever there is running water, like an ocean beach or near a waterfall.