It is perhaps less likely that vitamin D deficiency influences anti-TNF treatment responses in rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, psoriasis, hidradenitis suppurativa, and uveitis because these conditions are not associated with intestinal malabsorption of dietary vitamin D. Whether our findings are generalizable to other anti-TNF drugs, including certolizumab, golimumab, etanercept, and other biologicals, is unknown. Here, TNF is linked to ankylosing spondylitis.