Not just any vitamin D, it has to be D3, and it needs to be at least 2,000 I.U. daily. I take 5,000 I.U. daily. Furthermore, vitamin D3 has a very long half life (21 days for oral D3 supplements), it will take another three months before you reach peak serum concentrations. Additionally, it takes about ten days for your body to process vitamin D3 into its active metabolite.

Not knowing any details about you, the most I would recommend is a loading dose of 8,000 I.U. daily for one month, and then 4,000 I.U. daily thereafter. Have your doctor check your calcifediol (25-hydroxycholecalciferol) and calcitriol (1,25-dihydroxycholecalciferol) levels in three months.

I would also add NAC (N-Acetyl Cysteine). The reason for this is the active metabolite of vitamin D3, calcitriol, is an astrocyte glutathione catalyst. I believe D3's ability to increase neural glutathione is its principal mechanism of action, and cysteine is usually the rate limiting factor in glutathione production. NAC provides a source of cysteine, try 1200 mg daily for a month. Cysteine also participates in the NMDA system, NMDA receptor dysfunction is believed to be responsible for a number of negative symptoms in bipolar, schizoaffective, and schizophrenia like disorders. i.e. depressive, avolition type symptoms.

• N-acetylcysteine in psychiatry: current therapeutic evidence and potential mechanisms of action
• Regulation of Neuronal Glutathione Synthesis
• 1,25-Dihydroxyvitamin D3 Regulates the Synthesis of γ-Glutamyl Transpeptidase and Glutathione Levels in Rat Primary Astrocytes
• Thinking Outside the Cleft to Understand Synaptic Activity: Contribution of the Cystine-Glutamate Antiporter (System xc−) to Normal and Pathological Glutamatergic Signaling
• Glutathione in the Nervous System: Roles in Neural Function and Health and Implications for Neurological Disease