Vitamin K deficiency from long-term warfarin anticoagulation does not alter skeletal status in male rhesus monkeys

Abstract

Vitamin K (K) inadequacy may cause bone loss. Thus, K deficiency induced by anticoagulants (e.g., warfarin) may be an osteoporosis risk factor. The skeletal impact of long-term warfarin anticoagulation was evaluated in male monkeys. No effect on BMD or bone markers of skeletal turnover was observed. This study suggests that warfarin-induced K deficiency does not have skeletal effects.

Introduction: The skeletal role of vitamin K (K) remains unclear. It is reasonable that a potential role of vitamin K in bone health could be elucidated by study of patients receiving oral anticoagulants that act to produce vitamin K deficiency. However, some, but not all, reports find K deficiency induced by warfarin (W) anticoagulation to be associated with low bone mass. Additionally, epidemiologic studies have found W use to be associated with either increased or no change in fracture risk. Such divergent results may imply that human studies are compromised by the physical illnesses for which W was prescribed.

Materials and methods: To remove this potential confounder, we prospectively assessed skeletal status during long-term W anticoagulation of healthy nonhuman primates. Twenty adult (age, 7.4-17.9 yr, mean, 11.7 yr) male rhesus monkeys (Macaca mulatta) were randomized to daily W treatment or control groups. Bone mass of the total body, lumbar spine, and distal and central radius was determined by DXA at baseline and after 3, 6, 9, 12, 18, 24, and 30 mo of W treatment. Serum chemistries, urinary calcium excretion, bone-specific alkaline phosphatase, and total and percent unbound osteocalcin were measured at the same time-points. Prothrombin time and international normalized ratio (INR) were monitored monthly. Serum 25-hydroxyvitamin D was measured at the time of study conclusion.

Results: W treatment produced skeletal K deficiency documented by elevation of circulating undercarboxylated osteocalcin (8.3% W versus 0.4% control, p<0.0001) but did not alter serum markers of skeletal turnover, urinary calcium excretion, or BMD.

Conclusions: In male rhesus monkeys, long-term W anticoagulation does not alter serum markers of bone turnover or BMD. Long-term W therapy does not have adverse skeletal consequences in primates with high intakes of calcium and vitamin D.