Signs you are deficient in vitamin D. Number one, fatigue. Vitamin D deficiency may be the main reason why you feel fatigued. To help with this, you can take 5,000 IUs of vitamin D per day, first thing in the morning with magnesium. Number two, brain fog. Vitamin D helps regulate serotonin and dopamine, which are crucial for giving you focus and energy. These also affect mood. If you’re deficient in vitamin D, yeah, those neurotransmitters will not be firing. But vitamin D can disrupt this balance and make you feel off or giving you that off feeling. Number three, frequent illness. Vitamin D deficiency is known for getting you sick more often. Make sure you’re monitoring yourself through the year on how much you get sick. And also just take vitamin D because here