The vitamin D number your doctor calls fine

October 6, 2026

The vitamin D number your doctor calls fine

Thirty is the floor, not the goal. As the days get shorter, this is the lab worth checking before the flare arrives.

Author

Dr. Rodger Murphree
October 05, 2026

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Every year around this time my inbox fills with the same message. The pain is creeping back. Sleep is worse. Mood is heavier. Nothing changed except the light.

Something did change, though, and it is measurable.

You Stopped Making It in August

Your skin manufactures vitamin D when ultraviolet B rays hit it. Above roughly the latitude of Atlanta, the sun does not sit high enough in the sky from about October through March for that reaction to happen at all. You can stand outside all afternoon in January and produce essentially none.

Whatever level you have going into fall is what you will be drawing down from for the next six months. Which is why late summer is the right moment to look at it, not February when you are already in the hole.

Several things make the drop steeper. Darker skin requires substantially more sun exposure to make the same amount. Sunscreen blocks the reaction. Being indoors most of the day does the obvious. And carrying extra weight matters, because vitamin D is fat-soluble and gets sequestered in fat tissue where it is less available.

Not Really a Vitamin

The name is a historical accident. Vitamin D behaves like a hormone, and receptors for it appear on cells throughout the body, including immune cells, muscle cells, and nerve tissue.

That is why deficiency does not present as one clean symptom. It shows up as diffuse muscle aching that gets blamed on age. As frequent infections that take too long to clear. As low mood in the darker months. As bone and joint pain. As poor sleep.

Every one of those overlaps with what my patients already deal with, which makes low vitamin D one of the easier things to miss and one of the easier things to correct.

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Mental Health May Have More Than One Piece

Why 32 Is Not a Good Number

Most labs flag deficiency below 30 ng/mL. So a result of 32 comes back unflagged and the conversation ends.

But 30 was set as the threshold for preventing rickets and obvious bone disease. It is a floor for avoiding overt illness, not a target for feeling well. In my practice I want patients between 50 and 80 ng/mL, and the difference between 32 and 60 is something people frequently notice.

Ask for the actual number. The word normal is doing a lot of work in that sentence and very little of it is useful to you.

What This Means for You

  • Get the 25-hydroxy vitamin D test now. That is the specific test name. Testing in late summer tells you where you are starting from.

  • Take D3, not D2. D3 raises blood levels more effectively and is the form your skin makes.

  • Pair it with vitamin K2 and magnesium. K2 directs calcium into bone rather than arteries. Magnesium is required to convert vitamin D into its active form, which is why some people supplement for months and see almost no change in their level.

  • Take it with a meal that contains fat. Absorption drops substantially on an empty stomach.

  • Retest in three months. Individual response varies enormously. Two people on the same dose can land in very different places, and guessing is how people end up either under-dosed or higher than they need to be.

The Bottom Line

The seasonal decline that so many of my patients experience is not entirely in the weather. Some of it is a hormone your body simply stops producing when the sun drops below a certain angle. Check the number, aim above the minimum, and give the supplement the cofactors it needs to work.

Brought to you by or sponsored by Essential Therapeutics and essentialtherastore.com, physician formulated, pharmaceutical grade, clinically proven supplements for optimal cellular health.

Note: This newsletter is for education. Do not change or stop any medication without speaking with your doctor.