Researchers from Poland recently assessed the effect of tailored vitamin D supplementation based on deficiency level. The study, published in the journal Nutrients, considered BMI and genetic factors in order to optimize both skeletal and immune health.
The aim, according to the researchers, was to investigate the effects of long-term supplementation with low doses of vitamin D on calcium-phosphate metabolism and selected inflammatory cytokines.
Vitamin D deficiency
Vitamin D deficiency affects the global population, with as many as 80% of people estimated to be living with suboptimal serum 25(OH)D levels. This deficiency can cause osteomalacia in adults and rickets in children and contributes to various illnesses, including autoimmune disorders and cardiovascular issues.
The body synthesizes calcitriol, the biologically active form of vitamin D, through two hydroxylation steps in the liver and kidneys. Calcitriol influences the immune system by regulating cytokine expression and immune cell activity.
Vitamin D regulates T-cell differentiation, suppresses Th1 responses and promotes Th2 development, protecting against autoimmune diseases. It also reduces Th17 cell activity, which drives inflammation and autoimmune disorders.
Vitamin D also interacts with transforming growth factor beta (TGF-β) to regulate cell growth and differentiation and modulates immune function by impacting macrophages and B cells.
Previous research has highlighted vitamin D’s essential roles in bone metabolism, immune system function and preventing autoinflammatory diseases. However, the authors of the new study emphasize the need for further research to determine optimal dosing and better understand its immunoregulatory and bone-protective effects.
Tailored vitamin D supplementation
The study recruited 35 healthy volunteers, all of whom completed questionnaires on demographics, sunlight exposure and dietary habits.
Participants were divided into different classifications of vitamin D status: sufficient (≥75 nmol/L), insufficient (50–75 nmol/L), deficient (25–50 nmol/L) and severely deficient (0–25 nmol/L).
Those with suboptimal vitamin D levels (anything below 75 nmol/L) received supplementation (500–1,000 IU/day) for 12 months, with doses tailored to baseline levels.
The researchers found that year-long supplementation increased average vitamin D levels but did not reach the recommended levels. However, it improved bone health markers and reduced the hormone PTH, which can harm bones when too high.
Supplementation also reduced inflammatory cytokines and supported an anti-inflammatory response in immune cells. Specifically, the anti-inflammatory cytokine IL-10 levels remained stable, and pro-inflammatory IL-17 levels stayed low, aligning with vitamin D’s anti-inflammatory effects.
Furthermore, TGF-β which is important for immune regulation levels was maintained, and the pro-inflammatory cytokine IFN-γ levels decreased, showing anti-inflammatory benefits.
The researchers also found that higher doses and frequent administration may be better for correcting deficiencies. They also noted that bodyweight influences the efficacy of supplementation, observing lower effects in overweight individuals.
The researchers noted that current guidelines for supplementation vary widely and mostly prioritize calcium and phosphate management, rarely considering the immunomodulatory effects of calcitriol.
They concluded that tailored vitamin D supplementation showed skeleton-protecting effects, evident in reduced PTH and calcium levels, but that “further research is necessary to develop an algorithm for vitamin D supplementation”.
Source: Nutrients 2025, 17(2), 352. doi: 10.3390/nu17020352. “Does Systematic Use of Small Doses of Vitamin D Have Anti-Inflammatory Effects and Effectively Correct Deficiency Among Healthy Adults?”. Authors: Walawska-Hrycek, A. et al.