How Obesity Alters Vitamin D Supplementation in Osteoporosis
New insights suggest patients with obesity need higher and longer vitamin D dosing to protect bone health
Emerging research presented at the 2025 AACE conference reveals that individuals with obesity and osteoporosis may require significantly higher and prolonged doses of vitamin D3 to reach therapeutic serum levels challenging current one-size-fits-all supplementation guidelines.
Study Details
Vitamin D supplementation is a standard strategy for managing osteoporosis, essential for maintaining bone density and reducing fracture risk. However, clinicians have long observed that patients with obesity often show persistently low serum 25-hydroxyvitamin D levels despite supplementation. At the 2025 annual meeting of the American Association of Clinical Endocrinology (AACE), researchers from Tufts University highlighted how obesity alters vitamin D metabolism and absorption bringing new urgency to personalized supplementation strategies for this population.
Methodology
Findings discussed stem from both observational data and results from the STOP IT study, which followed adults aged 65 and older who were treated with 700 IU of vitamin D3 and calcium citrate malate over three years. Stratification of this data by BMI revealed that individuals with obesity not only started with lower vitamin D levels but also took much longer to achieve a steady state even up to 12 months.
Key Findings
People with obesity may need 40% to 200% more vitamin D compared to those with normal weight to reach target serum levels.
Obesity affects vitamin D status due to multiple mechanisms, including lower dietary intake, decreased sun exposure, altered enzymatic activity, and changes in gut microbiota.
Vitamin D levels in obese patients may continue rising for 12 months, indicating a delayed steady state compared to 6 months in normal-weight individuals.
Standard doses (1,000–2,000 IU/day) may be insufficient; weight-based dosing formulas or 2–3x higher doses may be required.
Overcorrection should be avoided, as excessive vitamin D can paradoxically increase fall and fracture risk.
Implications for Practice
For healthcare providers, these findings emphasize the importance of adjusting vitamin D supplementation based on body weight and monitoring levels over an extended period potentially up to 12 months in patients with obesity and osteoporosis.
For patients, this means that standard doses might not be enough, and longer-term monitoring is crucial. Patients should not assume rapid results from supplementation and must follow personalized plans developed by their provider.
Researchers noted, future guidelines may need to offer BMI-specific dosing recommendations, shifting the paradigm of osteoporosis care for millions of people affected by both obesity and vitamin D deficiency.