Sex-specific relationship between serum 25-hydroxyvitamin D concentrations and antinuclear antibodies in U.S. adults, NHANES 2001–2004

Table 3 Threshold effect analysis of serum 25 (OH) D levels and the risk of ANA positivity using Piece-wise Linear regression

Outcome	Adjusted OR (95%CI)	p-value
Fitting by a standard linear model	0.97 (0.95, 0.99)	0.0052
Fitting by two-piecewise linear models
Inflection point	18
25 (OH) D concentrations < 18 ng/mL	0.92 (0.87, 0.97)	0.0026
25 (OH) D concentrations ≥ 18 ng/mL	0.99 (0.96, 1.02)	0.5529
p for log-likelihood ratio	0.045

Adjusted for age, race, birth place, citizenship status, household number, cotinine, RA, taking prescribed medicine, kidneys disease

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