NOW Foods Calcium Citrate
vs
Douglas Laboratories K2-D3 with Astaxanthin
Supplement Comparison

  • Vitamin D: Douglas Laboratories K2-D3 with Astaxanthin has 3.3× more
  • The image below shows:
    • Side-by-side charts with label nutrient amounts, per serving
    • Nutrient forms as listed on the label
    • 16 nutrients compared
Bar chart: per-serving label amounts and listed forms for NOW Foods Calcium Citrate vs Douglas Laboratories K2-D3 with Astaxanthin.

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Frequently asked questions

Which active ingredients does NOW Foods Calcium Citrate have?

  • Vitamin D appears as Ergocalciferol (D2)
  • Calcium appears as Calcium Citrate
  • Magnesium appears as Magnesium Oxide
  • Zinc appears as Zinc Amino Acid Chelate
  • Copper appears as Copper Amino Acid Chelate
  • Manganese appears as Manganese Amino Acid Chelate

Which active ingredients does Douglas Laboratories K2-D3 with Astaxanthin have?

  • Vitamin D appears as Cholecalciferol (D3)
  • Vitamin K appears as Vitamin K2 trans MK-7 K2VITAL
  • Astaxanthin appears as AstaReal Astaxanthin (supercritical CO2 extract of Haematococcus pluvialis)

Which categories do NOW Foods Calcium Citrate and Douglas Laboratories K2-D3 with Astaxanthin belong to?

  • Mineral Complex
  • Single Mineral
  • Single Vitamin

What health concerns do NOW Foods Calcium Citrate and Douglas Laboratories K2-D3 with Astaxanthin address?

  • General Health
  • Heart & Cardiovascular Health
  • Joint & Bone Health
  • Antioxidant Support

Which product has a higher amount of Vitamin D per serving?

  • Douglas Laboratories K2-D3 with Astaxanthin has the highest total amount of Vitamin D: 2500 IU per serving

How do the serving sizes compare between the two supplements?

  • Serving size:
    • NOW Foods Calcium Citrate: 3 capsules
    • Douglas Laboratories K2-D3 with Astaxanthin: 1 capsule
  • Vitamin D
    • This supplement has 750 IU
    • Recommended Dietary Allowance in men: 600 IU
    • Recommended Dietary Allowance in women: 600 IU
    • Tolerable Upper Intake Level: 4000 IU
  • Calcium
    • This supplement has 450 mg
    • Recommended Dietary Allowance in men: 1000 mg
    • Recommended Dietary Allowance in women: 1000 mg
    • Tolerable Upper Intake Level: 2500 mg
  • Zinc
    • This supplement has 11 mg
    • Recommended Dietary Allowance in men: 11 mg
    • Recommended Dietary Allowance in women: 8 mg
    • Tolerable Upper Intake Level: 40 mg
  • Copper
    • This supplement has 0.75 mg
    • Recommended Dietary Allowance in men: 0.9 mg
    • Recommended Dietary Allowance in women: 0.9 mg
    • Tolerable Upper Intake Level: 10 mg
  • Manganese
    • This supplement has 4 mg
    • Adequate Intake in men: 2.3 mg
    • Adequate Intake in women: 1.8 mg
    • Tolerable Upper Intake Level: 11 mg
  • Vitamin D
    • This supplement has 2500 IU
    • Recommended Dietary Allowance in men: 600 IU
    • Recommended Dietary Allowance in women: 600 IU
    • Tolerable Upper Intake Level: 4000 IU
  • Vitamin K
    • This supplement has 180 mcg
    • Adequate Intake in men: 120 mcg
    • Adequate Intake in women: 90 mcg
    • Tolerable Upper Intake Level: Not established

Last updated: February 2, 2026

  • Sources & Methodology: Nutrient data and forms are taken directly from Supplement Facts labels. Reviewed and standardized by the VIOscan Research Team. Learn more on the Methodology page.
  • We show the Recommended Dietary Allowance (RDA) when available. If no RDA exists, we show the Adequate Intake (AI). Tolerable Upper Intake Levels (UL) are used for upper limits. Unless otherwise noted, RDAs shown correspond to healthy adults aged 19–50 years and are sex-specific. Separate values exist for 51–70 years and >70 years, and pregnancy and lactation are excluded. All values come from the Dietary Reference Intakes (DRIs) published by the National Academies of Sciences, Engineering, and Medicine (NASEM), Food and Nutrition Board (FNB).
  • Transparency: We’re funded by our users. We don’t have sponsors or affiliate links, and we don’t sell supplements.
  • Editorial standards: we provide independent, impartial and objective data analysis.
  • This analysis is for educational purposes only. It is not a substitute for medical advice.
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  • Author: VIOscan Research Team