Immune cell profile improves around 38–41 ng/mL of Vitamin D - observation of 316 healthy adults

Serum 25(OH)D concentrations are differentially associated with innate and adaptive immune cell markers, with threshold effects near 40 ng/mL: A cross-sectional study

Nutrition Research (Elsevier), October 2026, https://doi.org/10.1016/j.nutres.2026.08.001

Peng Lei, Shaoyan Wu, Rong Luo, Binyang Tang, Sicen Wu

Summary by Claude - September 2026

In healthy adults, higher vitamin D levels went along with more natural killer (NK) cells and a smaller share of T cells. The changes in these associations clustered around 38–41 ng/mL.

This was a cross-sectional study of 316 healthy adults who had routine health check-ups at a Chongqing, China hospital from 2022 to 2023. Immune cells were counted by flow cytometry. No vitamin D was given; the study looked only at existing serum 25(OH)D levels.

Participants above 28.45 ng/mL, compared with those below, had:

higher NK cell counts (306 vs 272.5) and NK percentage (15.5% vs 14.2%) a lower CD3+ T-cell percentage (70.0% vs 73.2%)

After adjustment, each ng/mL of 25(OH)D was associated with CD3+ T% lower by 0.16 points, NK count higher by 3.6 cells, and NK% higher by 0.16 points. Spline models found inflection points at 37.9 ng/mL (NK count) and 40.9 ng/mL (NK% and CD3+ T%). The associations were stronger in men and in people aged 40–59.

The authors interpret this as vitamin D boosting innate immunity while restraining adaptive immunity. They add that "causal relationships cannot be inferred from this cross-sectional design."

What this does not show / limitations:

• It does not show that immunity works better above 40 ng/mL.
• Only cell numbers were measured, not NK killing ability or infection outcomes.
• It is a single snapshot, so it cannot show that raising vitamin D changes immune cells.
• The higher-D group was older, more often male, and had a higher BMI. NK% and T% share one lymphocyte pool, so they partly move in opposite directions by arithmetic.
• Estimates near 40 ng/mL may rest on relatively few people, since the group split fell at 28.45 ng/mL. Only the article preview was reviewed here.

Partial PDF

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