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Vitamin D3 and K2 Supplementation Study for Healthcare Personnel

This study is looking at how vitamin D3 and vitamin K2 supplements affect your blood levels and the bacteria in your gut (gut microbiome). You might be eligible if you are a healthcare worker between 18 and 69 years old, can read English, and have low vitamin D levels (25 OHD serum level equal to or less than 30 ng/mL). You would need to stop taking any vitamin D3 or K2 supplements for 4.5 months before and during the study. Participants will take a capsule daily for 90 days, which could be vitamin D3, vitamin K2, a combination of both, or a placebo (an inactive substance). The main goal is to see how these supplements change the types and amounts of bacteria in your gut after 90 days.

Study design
This is an interventional study planning to enroll 96 participants. Participants will be assigned to one of four groups: vitamin D3, vitamin K2, a combination of D3 and K2, or a placebo.
What's involved
You will take a dietary supplement or placebo capsule daily for 90 days. You will also need to stop taking vitamin D3 and/or K2 supplements for 4.5 months.
Compensation
Not stated in the trial record.
Follow-up
Your gut microbiome composition, richness, and diversity will be measured at 90 days.

AI-generated from the public study record. Only the study team can confirm whether you're eligible — confirm details with them before making decisions.

NCT07199829

Evaluating Response to Vitamin D3 and K2 Supplementation in Healthcare Personnel

Recruiting
NAAges 18–69InterventionalTreatment
Madigan Army Medical Center
~96 participants
Updated 2025-09-30 on ClinicalTrials.gov
What's tested:Vitamin Arm 1Vitamin Arm 2Vitamin Arm 3Placebo

At a glance

Recruiting sites
1 of 1 listed site is recruiting right now
RecruitingSuspended, closed, or not yet open
What they're measuring
Gut microbiome composition
Measured over 90 days
+2 more outcomes measured

Conditions

Hypovitaminosis D
Hypovitaminosis

Explore related trials

Vitamin D DeficiencyVitamin Deficiency Disorder

NCT07199829

Where you'd take part

This study runs at 1 site. They're the same protocol — you choose where, and that choice sets who your contact draft is addressed to.

  • Madigan Army Medical Center

    Tacoma, Washingtonstudy coordinator listed

    Recruiting

Sites open and close at different times, so the status above is per site — it can differ from the study's overall status.

Study leadership

  • Mary S McCarthy, PhD · PRINCIPAL_INVESTIGATOR · Madigan AMC

Who to contact

Mary S McCarthy, PhD
[email protected]
253-968-3695
Email the study team

Opens a ready-to-send draft in your own email app — review before sending.

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Eligibility criteria

Inclusion

able to read and understand English
25 OHD serum level equal to or less than 30 ng/mL
willing to discontinue vitamin D3 and/or K2 supplements for 4.5 months
military beneficiary (Active Duty, Retired, Dependent)
remaining employed at workplace for 6 months

Exclusion

Diagnosed medical condition that prevents nutrient absorption from food (e.g. Inflammatory Bowel Disease, Celiac Disease, post-Roux-en-Y/Gastric sleeve surgery)
Pregnant or breastfeeding
Current antibiotic use or within past 3 months
Current anticoagulant use or within past 3 months
Current weight loss or fat malabsorption medication use (e.g. Glucagon-Like Peptide 1 agonists, Orlistat)
Allergies or sensitivities to methylcellulose, vitamin D (D3, D2), or vitamin K (K2, Menaquinone-4, Menaquinone-7)

What this trial measures

  • Gut microbiome composition90 days

    Evaluate effect of vitamin D3 and K2 dietary intake, and assigned vitamin supplementation group versus placebo group, on the gut microbiome composition

  • Gut microbiome richness90 days

    Will use Operational Taxonomic Units, Simpson Index and /or Chao1 index to evaluate gut microbiome richness before and after vitamin supplementation vs placebo

  • Gut microbiome diversity90 days

    Will use Operational Taxonomic Units, Simpson Index and /or Chao1 index to evaluate gut microbiome diversity before and after vitamin supplementation vs placebo