Absorption and Excretion of Vitamin K Varies by Age and Triglycerides: A Metabolic Study in Older and Younger Adults Using Deuterium‐Labeled Collard Greens

Abstract

Vitamin K is an essential fat‐soluble nutrient, with its most established role as a cofactor in coagulation. Emerging roles in soft tissue calcification have been proposed. However, further progress in understanding absorption and metabolism is needed, including knowledge of the factors influencing the physiologic response to vitamin K. Phylloquinone (PK) is the primary form of vitamin K in the diet and circulation. Large intra‐individual variances in circulating PK exist, and little is known about the dietary and non‐dietary factors that influence PK metabolism.The purpose of this study was to compare absorption efficiency and body retention of PK in older and younger adults following dietary vitamin K depletion and repletion.Forty‐two older (55–80 y; n=21) and younger (18–40 y; n=21) adults were maintained on sequential 28‐day vitamin K depletion (~10 ug PK/day) and vitamin K repletion (~500 ug PK/day) diets. At the end of each phase, subjects were fed deuterated collard greens (2H‐PK) and monitored over 72 hours. Liquid chromatography‐mass spectrometry (LC‐MS) was used to measure labeled and unlabeled PK in plasma and triglyceride‐rich lipoprotein (TRL) fractions, and labeled and unlabeled menadione (a PK metabolite) from 24‐hr urine collections.Absorption efficiency of 2H‐PK did not differ between PK depletion and repletion, but was significantly higher in older adults than in younger adults (p=0.02). 2H‐PK in TRL fractions was correlated with the total 2H‐PK in plasma (r=0.95, p<<0.001), corroborating previous data that PK is primarily transported in circulation associated with triglycerides. Age (p=0.015) and plasma triglycerides (p<0.001) were significant linear predictors of 2H‐PK area under the curve (AUC). Both age and plasma triglycerides retained significance in the multivariate model, and together explained 31.6% of the variance in absorbed plasma 2H‐PK during the depletion period, and 29.9% in the repletion period. Analysis of urinary 2H‐menadione showed no differences in body retention of vitamin K by age, sex, or depletion or repletion.In conclusion, age and circulating triglycerides are determinants of vitamin K absorption efficiency and together explained about 30% of the variance observed in absorbed PK. Body retention of vitamin K did not vary by age, sex, or dietary intake. There is a need to elucidate non‐traditional factors, such as genetics, that may influence absorption and metabolism of vitamin K.Support or Funding InformationStudy supported by the USDA ARS under Cooperative Agreement 58‐1950‐7‐707 and the NIH (5R01DK69341‐4).