Scientists give rats a lot of stress and then see what they can do to reduce stress hormones. Something that successfully lowers stress hormones is vitamin C.
Researcher P. Samuel Campbell and his colleagues found that 200 mg of vitamin C per day reduced the level of stress hormones in the rats' blood. That's a pretty big dose for a little critter. It is the equivalent of several grams of vitamin C per day for you or me, which is actually in the range of what the famous chemist, Linus Pauling recommended. It is also in the range of what chimpanzees — our closest genetic relatives — get in their daily diet in the wild.
Other things that indicated a generally lower stress level for the rats taking the vitamin C were: 1) their adrenal glands didn't enlarge as much as they normally do when rats are constantly stressed, 2) they didn't lose as much weight as the stressed but unmegadosed rats (stress tends to make people put on weight), and 3) their spleens and thymus glands didn't shrink as much.
I'm not a biochemist or a doctor. You can do your own research and draw your own conclusions. I'm noting it here because it is relevant to our topic (improving your mood by reducing stress and anxiety) and can give you an avenue to pursue you might not otherwise have thought about.
If you feel particularly stressed out, it probably wouldn't hurt to take some extra vitamin C and it might even help you feel better.