Primary Causes & Action Plans

Vitamin D

Regulates serotonin and dopamine synthesis throughout the brain
Vitamin D deficiency is one of the strongest biochemical correlates of depression. Vitamin D is a neurohormone that regulates neurotransmitter synthesis and modulates the immune response. Up to 80% of people with depression are vitamin D deficient.
Target > 50 ng/mL (> 125 nmol/L)
Suggested Action Plan

If deficient, supplement with vitamin D3 4000-5000 IU daily. Get 20-30 minutes of midday sun exposure 3-4 times per week. Retest in 8-12 weeks. Once optimal, maintain with 2000-3000 IU daily.

Thyroid Panel (TSH/Free T4)

Thyroid hormones regulate neurotransmitter synthesis and cerebral blood flow
Hypothyroidism is a common cause of depression, especially in women. Even subclinical hypothyroidism (elevated TSH, normal T4) causes depressed mood. Both TSH and free T4 should be tested and optimized.
Target TSH: 1.0-2.5 mIU/L; Free T4: 1.0-1.5 ng/dL
Suggested Action Plan

If thyroid function is low, thyroid hormone replacement is necessary. Levothyroxine is first-line; some people respond better to combination levothyroxine/liothyronine. Work with a thyroid-savvy doctor. Retest in 6-8 weeks after treatment adjustment.

Vitamin B12

Essential for monoamine neurotransmitter synthesis
B12 deficiency impairs dopamine and serotonin synthesis and elevates homocysteine (which damages neurons directly). B12 deficiency is common in vegans, vegetarians, and those over 50. Supplementing B12 often resolves depression within weeks.
Target > 500 pg/mL
Suggested Action Plan

If B12 is low, supplement with methylcobalamin 1000-2000 mcg daily or 1000 mcg weekly injections. Injections work faster if absorption is impaired. Retest in 3 months after supplementation begins.

Folate (B9)

Critical cofactor for serotonin synthesis; deficiency is common in depression
Folate (the natural form of B9) is required for methylation and monoamine neurotransmitter synthesis. Deficiency is associated with depression and mood disorders. Many antidepressants work better when folate levels are adequate.
Target > 8 ng/mL (> 20 nmol/L)
Suggested Action Plan

If folate is low, supplement with methylfolate (not folic acid) 800-1000 mcg daily. Increase dietary folate: leafy greens, legumes, asparagus. Retest in 4-8 weeks.

Testosterone (Free & Total)

Regulates mood, motivation, and dopamine sensitivity; deficiency causes depression
Low testosterone is associated with depression, low motivation, and anhedonia (loss of pleasure). Both men and women need adequate testosterone for optimal mood. Many depressed individuals have never had testosterone tested.
Target Total: 500-900 ng/dL (men); 15-70 ng/dL (women). Free: 9-30 pg/mL (men)
Suggested Action Plan

If testosterone is low, work with a hormone-knowledgeable doctor on testosterone replacement therapy (TRT). This often produces rapid mood improvement. Retest 6-8 weeks after treatment starts.

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Getting Started

1
Get Comprehensive Nutrient & Hormone Testing

Do not accept a depression diagnosis based on symptoms alone. Test vitamin D, B12, folate, thyroid panel, and testosterone. At least one—usually more—will be abnormal. Fix the metabolic problem, and depression often resolves.

2
Prioritize Vitamin D Repletion

Vitamin D deficiency is the strongest biochemical correlate of depression. If your vitamin D is low, aggressive repletion (4000-5000 IU daily) should be your first intervention. Many people see mood improvement within 2-4 weeks.

3
Address All Deficiencies Simultaneously

Do not fix vitamin D and ignore B12 or thyroid dysfunction. These nutrients work synergistically; addressing one without the others limits your recovery. Target all identified deficiencies.

4
Give Metabolic Treatment 8-12 Weeks

Psychiatric antidepressants take 6-12 weeks to work. Metabolic treatment deserves the same timeframe. Track your mood daily and retest biomarkers after 8-12 weeks. You should see both biochemical and mood improvement.

5
Add Psychological Intervention if Needed

Metabolic optimization is often sufficient. But if depression persists after 12 weeks of target treatment, psychotherapy (CBT, DBT) or medication may be helpful. The combination of optimized metabolism plus therapy is more powerful than either alone.

Why I built this guide.

"Depression is a symptom of multiple underlying conditions, not a single psychiatric disease. Test metabolic causes before assuming you need psychiatric medication."

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