Magnesium is one of those nutrients clinicians think they understand—until they take a closer look. In this episode, we sit down with Dr. Robert Fredrickson, author of Magnesium Answers, to unpack why this foundational mineral continues to create confusion in modern practice. We explore the gap between what standard lab testing shows and what may be happening intracellularly, how lifestyle factors like stress may influence magnesium balance, and how to think more precisely about selecting the right form for the patient in front of you. This conversation is a reminder that advancing patient care isn’t always about adding more complexity—it’s about seeing the fundamentals more clearly.

Why serum magnesium may not reflect total body or intracellular magnesium status

• Serum magnesium represents a small fraction of total body stores, which may limit its utility as a standalone marker; intracellular measures like RBC magnesium may offer additional insight (NIH, 2022).

Magnesium’s foundational role in ATP production and metabolic processes.

• Magnesium is required as a cofactor in ATP synthesis and numerous enzymatic reactions, supporting energy metabolism and overall cellular function (Gröber et al., 2015).

Magnesium as a cofactor in vitamin D metabolism and nutrient synergy.

• Magnesium participates in multiple steps of vitamin D activation, highlighting the importance of evaluating nutrient interactions in clinical planning (Uwitonze & Razzaque, 2018).

Dr. Robert Fredrickson is a clinician, educator, and author of Magnesium Answers: Unlocking the Secrets of Magnesium. With a background in sports medicine and functional medicine, he focuses on helping clinicians better understand mineral balance, metabolic health, and evidence-informed supplementation strategies. He also works with Fullscript, supporting providers with clinical decision support and access to professional-grade supplements and nutraceuticals. Dr. Fredrickson also has his own podcast, the Fredrickson Health Show.

• Not always. Serum magnesium reflects a small percentage of total body magnesium
• Intracellular markers, such as RBC magnesium, may provide additional context
• Interpreting trends alongside clinical presentation may support decision-making (NIH, 2022)

• Dietary intake and food quality
• Malabsorptive disorders like celiac and IBD
• Alcohol intake
• Insulin resistance or type 2 diabetes
• Vitamin D deficiency (NIH, 2022)



• Magnesium acts as a cofactor in enzymes required for vitamin D metabolism
• Inadequate magnesium status may influence how vitamin D is processed in the body (Uwitonze & Razzaque, 2018)

• 00:00 – Why magnesium remains overlooked in modern clinical care
• 02:20 – Dr. Fredrickson’s shift from sports medicine to functional medicine
• 05:32 – Limitations of serum magnesium testing in clinical practice
• 07:27 – Understanding intracellular magnesium and RBC testing
• 09:51 – Magnesium’s role in ATP production and metabolic function
• 13:25 – Dietary patterns, food quality, and nutrient density challenges
• 15:55 – How to select the appropriate form of magnesium
• 18:33 – Magnesium citrate and GI motility considerations, including GLP-1 support
• 20:46 – Common clinical patterns associated with low magnesium status
• 22:09 – Safety considerations and when to individualize magnesium use

This episode is sponsored by Fullscript, a comprehensive care delivery platform designed to support whole-person, integrative healthcare. Fullscript allows clinicians to streamline supplement dispensing, lab ordering, and patient education in one free, centralized system—helping reduce administrative burden while supporting clinical decision-making. For practitioners, Fullscript offers access to professional-grade supplements, evidence-informed protocols, and lab integrations that can support more efficient planning and follow-up. For patients, it provides a clear, organized way to receive recommendations, manage refills, and stay engaged in their care. The goal is not to replace clinical judgment, but to make it easier for clinicians to focus on what matters most: thoughtful, individualized patient care.

The views expressed on this podcast are those of the hosts and guests and don’t necessarily reflect those of Fullscript or any affiliated organizations. This podcast is for informational and educational purposes only and is not intended to be medical advice. For your safety, always check with your doctor or healthcare provider before making changes to your health routine.

1. Gröber U, Schmidt J, Kisters K. Magnesium in Prevention and Therapy. Nutrients. 2015 Sep 23;7(9):8199-226. doi: 10.3390/nu7095388. PMID: 26404370; PMCID: PMC4586582.
2. Rosanoff A, Weaver CM, Rude RK. Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutr Rev. 2012 Mar;70(3):153-64. doi: 10.1111/j.1753-4887.2011.00465.x. Epub 2012 Feb 15. PMID: 22364157.
3. Uwitonze AM, Razzaque MS. Role of Magnesium in Vitamin D Activation and Function. J Am Osteopath Assoc. 2018 Mar 1;118(3):181-189. doi: 10.7556/jaoa.2018.037. PMID: 29480918.
4. National Institutes of Health. “Magnesium.” National Institutes of Health, 2022, ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/.