The brain chemical Serotonin is maybe the most important of the chemicals because it is involved in both anxiety and depression.    Serotonin levels can dip from chronic inner or external stress thus leading to anxiety.  The 2 most effective natural things that I do to control my anxiety are vigorous aerobic exercise (I’m a runner) and lots of time outdoors in the sunlight.   Both of these release serotonin which calms you and helps with a positive mood.  I also cut out caffeine because a stimulant makes anxiety much worse.  For very serious cases of anxiety, medication may be needed.