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Vitamin D

Designed for a 60-second scan in primary care. Use this to explain why this theory fits, what would weaken it, and which tests are most worth discussing.

Why this still fits

I want to check my vitamin D level against the range associated with cognitive health, not just the standard lab normal. I also want to check magnesium and PTH because vitamin D metabolism depends on both, and I may be repleting D without addressing the root problem.

What would weaken it

  • -Vitamin D levels are adequate and there's no deficiency context or broader depletion pattern.
  • -Correcting the deficiency doesn't change anything and another cause fits the symptoms better.
  • -The fog behaves more like sleep, thyroid, anemia, or depression than like a simple nutrient issue.

Key points to communicate

  • •I want to know whether low vitamin D is actually driving the fog or just showing up as one piece of a larger deficiency picture.
  • •Please separate vitamin D deficiency from iron, B12, thyroid, mood, and sleep overlaps.
  • •If vitamin D is relevant, I want realistic expectations for how much improvement to expect and when.

Bring this to the visit

  • •25-hydroxyvitamin D level with the date it was drawn.
  • •Current vitamin D supplementation: dose, form (D2 vs D3), and whether taken with fat.
  • •Geographic location, skin tone, sun exposure estimate, and season.
  • •Co-occurring conditions: autoimmune disease, malabsorption, kidney disease, obesity.

Useful screening structure

  • -25-hydroxyvitamin D (the correct test - not 1,25-dihydroxyvitamin D).
  • -Calcium and PTH if vitamin D is severely low to assess bone health impact.
  • -Magnesium level since magnesium is needed for vitamin D metabolism.

Tests and measurements to discuss

25-OH Vitamin D

What this helps clarify: Severe deficiency doubles dementia risk

Range context

40–60 ng/mL

How to use the result

Save the result with date and symptoms from the same week.

PTH (parathyroid hormone)

RBC Magnesium

What this helps clarify: Intracellular magnesium - serum levels miss deficiency

Range context

5.0–6.5 mg/dL

How to use the result

Save the result with date and symptoms from the same week.

Questions to ask directly

  • •What's my target vitamin D level for symptom resolution - is 40-60 ng/mL the goal?
  • •Should I take a loading dose followed by maintenance, and what dose is appropriate for my level?
  • •Could malabsorption explain why my level isn't responding to supplementation?
  • •Are there co-occurring deficiencies (magnesium, K2, iron) we should address alongside vitamin D?

Functional impact snapshot

  • -Track fog severity before and during supplementation over 8-12 weeks.
  • -Rate whether energy and mood improve alongside cognition as vitamin D level rises.
  • -Note seasonal patterns: is the fog worse in winter months with less sun exposure?

Escalate instead of self-managing if

  • •Severe deficiency (<10 ng/mL) with bone pain, muscle weakness, or fractures.
  • •Hypercalcemia symptoms from excessive supplementation: nausea, confusion, kidney stones.
  • •Progressive cognitive decline disproportionate to vitamin D level - investigate other causes.

Peer-reviewed references

  1. 1. Demay MB et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024;109(8):1907-1947 [DOI]
  2. 2. Ghahremani M et al. Vitamin D supplementation and incident dementia: Effects of sex, APOE, and baseline cognitive status. Alzheimers Dement (Amst). 2023;15(1):e12404 [DOI]
  3. 3. Anglin RES, Samaan Z, Walter SD, McDonald SD. Vitamin D deficiency and depression in adults: systematic review and meta-analysis. Br J Psychiatry. 2013;202:100-107 [DOI]