Here's an analysis of your current supplement stack, with a summary of the potential benefits, typical dosages, and interactions based on current scientific knowledge:

1. Collagen (10g/day):

   • Benefits: Supports skin health, joint, and bone health¹². However, the impact on skin and joint health may be limited since the body breaks it down into amino acids and reuses it².
   • Dosage: Commonly recommended at about 2.5 to 10 grams per day for skin benefits³.

2. Creatine (5g/day):

   • Benefits: Enhances muscle performance, strength, and exercise recovery⁴⁵.
   • Dosage: Typically, 3-5 grams daily is effective for maintaining muscle creatine stores⁶.

3. Glutamine (5g/day):

   • Benefits: Supports gut health and immune function. It may be beneficial for muscle recovery⁷.
   • Dosage: Often used in dosages up to 10 grams daily⁸.

4. Leucine (1.8g/day):

   • Benefits: Essential amino acid important for muscle protein synthesis⁹.
   • Dosage: Effective doses range from 2.5 to 5 grams to optimally stimulate muscle protein synthesis⁹.

5. Ashwagandha (200mg/day):

   • Benefits: Known for reducing stress and anxiety. It can also improve sleep and cognitive function¹⁰¹¹.
   • Dosage: Effective doses typically range from 300 to 600 mg daily¹¹.

6. L-Theanine (200mg/day):

   • Benefits: May help reduce stress, anxiety, and improve sleep quality¹²¹³.
   • Dosage: Commonly used in dosages of 100-300 mg¹².

7. Magnesium (200mg/day):

   • Benefits: Supports muscle and nerve function, energy production¹⁴.
   • Dosage: The recommended daily allowance is 400-420 mg for men and 310-320 mg for women¹⁵.

8. Vitamin D3 (400 IU/day):

   • Benefits: Important for bone health and immune function¹⁶¹⁷.
   • Dosage: Doses of 800-1000 IU/day are often recommended for optimal blood levels¹⁸.

9. Iron (7mg/day):

   • Benefits: Essential for hemoglobin and red blood cell function¹⁹.
   • Dosage: Women may need up to 18 mg/day; men typically need 8 mg/day²⁰.

10. Zinc (7mg/day):

    • Benefits: Supports immune function and wound healing²¹.
    • Dosage: Recommended dietary allowance is 8-11 mg/day depending on age and gender²².

11. Calcium (250mg/day):

    • Benefits: Important for bone health²³.
    • Dosage: The total daily intake should be 1000-1200 mg from all sources²³.

12. Berberine (500mg with high-carb meals):

    • Benefits: May help regulate blood sugar levels and improve cholesterol²⁴.
    • Dosage: Commonly used in doses of 500 mg 2-3 times daily²⁵.

13. Melatonin (3mg for poor sleep):

    • Benefits: Can improve sleep onset and quality²⁶.
    • Dosage: Typically, 1-5 mg is effective²⁷.

Regarding Vitamin D3 and K2:

• Interaction: Vitamin K2 is thought to work synergistically with D3 in maintaining bone health, as K2 helps direct calcium to bones²⁸²⁹. If your diet provides adequate vitamin K through leafy greens and fermented foods, additional supplementation may not be necessary.

Regarding Multivitamins:

• They can help fill nutritional gaps, but if your diet is varied and nutrient-rich, they may not be necessary. Individual needs can vary based on diet, health status, and lifestyle.

Your stack covers many essentials, but make sure your dietary sources complement these supplements. Always consider consulting with a healthcare provider to tailor supplementation to your specific health needs.