New Vitamin D & Immune System Study

The new Danish RCT, combined with a previous Chinese trial, demonstrates that supplementation with ~800–1,000 IU during winter lowers respiratory infection incidence and severity. The effect is conditional: children whose levels drop below 50 nmol/L benefit, while those who maintain >92 nmol/L (as in the Canadian study) do not. The Endocrine Society cautiously endorses this use. Stanfield applies this protocol to his own three children.

Observational studies once suggested widespread benefits, but large trials like VITAL and a 2024 meta-analysis found no reduction in heart attacks, cancer, or all-cause mortality with supplementation. Consequently, the 2024 Endocrine Society guidelines scaled back recommendations to 600–800 IU, enough to prevent nutritional deficiency and the known harms of hypovitaminosis D while avoiding the dangers of supra-physiological doses. Stanfield now follows this threshold.

A Canadian three-year trial compared 400 IU, 4,000 IU, and 10,000 IU of vitamin D daily. The 4,000 IU group lost 2.4% wrist bone density, and the 10,000 IU group lost 3.5%. Additionally, studies link high vitamin D with falls, potentially due to muscle weakness. This runs counter to the social media narrative pushing mega-doses. Stanfield now ensures his own supplement stays at 1,000 IU. The Endocrine Society’s revised lower recommendations reflect this risk.

The trial enrolled 189 children in Denmark, where winter sunlight is scarce, causing natural vitamin D drops. The supplementation group received 1,000 IU (25 µg) daily vs placebo. Outcomes: 17% fewer sick days from all respiratory infections, and 43% fewer days with fever. The authors purposely targeted an effective dose around 800 IU; they chose 1,000 IU because children miss doses, netting an average 800 IU/day. This dose aligns with their earlier research showing 800 IU maintained normal immune responses while 400 IU did not. The Canadian trial that showed no benefit had post-study vitamin D levels of 92 nmol/L even in the low-dose group – higher than the Danish children's starting levels – meaning they were already sufficient. Thus, vitamin D supplementation only helps when levels would otherwise fall below the deficiency threshold (~50 nmol/L). This adds confidence to the Endocrine Society’s cautious endorsement, and Stanfield now supplements his own children accordingly.

After reviewing the 2024 Endocrine Society guidelines, which lowered the recommended intake for the general population to 600–800 IU daily, Stanfield changed his personal supplement formulation. He dropped the vitamin D content from 2,000 IU to 1,000 IU per daily dose. He also explained that recent evidence shows a relationship between vitamin D, vitamin K2, and magnesium, which is why he kept those in the product. He is transparent that he personally takes this supplement but does not mean the viewer should necessarily do the same, underscoring the risk of excessive intake.