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Purpose: Obese populations have demonstrated lower levels of 25-hydroxyvitamin D compared to non-obese subjects, yet it is unclear whether obese patients require greater amounts of vitamin D supplementation to achieve adequate repletion. The objective of this study was to compare the response to vitamin D supplementation between obese and non-obese patients based on 25-hydroxyvitamin D levels.
Methods: Patients treated in a lipid specialty clinic who were over 18 years of age, had a documented low baseline 25-hydroxyvitamin D level, received vitamin D supplementation, and had a documented follow-up 25-hydroxyvitamin D level from January 1, 2007 to December 31, 2011 were included. Key exclusion criteria included history of osteoporosis, organ transplant/dysfunction, thyroid disorder, gastric bypass, hyperphosphatemia, and chronic kidney disease. Patients with a body mass index (BMI) >30 kg/m2 were classified as obese, whereas those <30 kg/m2 were considered non-obese.
Results: Data from 66 non-obese and 92 obese patients were analyzed. The groups differed significantly in regards to mean BMI (26.5 kg/m2 vs. 34 kg/m2, p<0.001), and those considered obese had higher rates of hypertension, diabetes, and metabolic syndrome (p<0.001). Mean baseline 25-hydroxyvitamin D levels were similar in both groups (20 ng/ml vs.18 ng/ml; p=0.094). Groups were prescribed similar mean initial bolus (loading) dosing (48,400 units/day vs 51,680 units/day; p=0.405) and maintenance dosing (2707 units/day vs. 3181 units/day; p=0.284). Duration of bolus dosing (10 days vs. 11 days; p=0.236) and maintenance dosing (188 days vs. 168 days; p=0.290) was similar in both groups, as was mean follow up 25-hydroxyvitamin D levels after supplementation (40.4 ng/ml vs. 38 ng/ml; p=0.290).
Conclusion: Non-obese and obese patients had similar rates of vitamin D deficiency and did not require significantly different amounts or duration of vitamin D supplementation to achieve repletion. More information is required before modifying vitamin D supplementation regimens based on patient weight.