Fatigue is a symptom of many diseases and deficiencies, but when coupled with these other signs, it can help you spot a vitamin C deficiency. Vitamin C plays a key role in energy production and mood stabilization, so a lack of vitamin C can throw both your energy and mood out of balance. There is evidence that eating produce high in vitamin C can enhance overall mood, reduce fatigue, increase vigor, and reduce depression. Watch for these other signs you’re running low on key nutrients.