Dietary intake and adequacy of vitamin K

A comprehensive review of vitamin K and vitamin K antagonists

For more than 60 years, vitamin K-dependent proteins have been known to play an important role in regulating blood coagulation. During recent years it has become clear, however, that vitamin K is also involved in other physiologic processes, including bone metabolism and vascular biology. Because the vitamin K requirement of bone and vessel wall is higher than that of the liver (where the clotting factors are produced) recommended daily allowance (RDA) values for K vitamins must be redefined. According to the new definition, a substantial part of the population is mildly deficient in vitamin K, and at later ages this deficiency may contribute to increased bone fracture risk, arterial calcification, and cardiovascular disease.

Warfarin use and fracture risk

Two recent studies examined the association between chronic use of warfarin, a vitamin K antagonist, and fracture rate among older women. Whereas one study reported no association, the other reported a significantly higher risk for vertebral and rib fractures among warfarin users compared with nonusers. The effect of vitamin K antagonists on age-related bone loss continues to be controversial.

Response of vitamin K status to different intakes and sources of phylloquinone-rich foods: comparison of younger and older adults

BACKGROUND

Phylloquinone, found in dark-green vegetables and certain plant oils, is the primary dietary source of the fat-soluble vitamin K. Limited data suggest that the relative bioavailability of phylloquinone from vegetables is lower than that from a supplement. This finding is relevant to the maintenance of optimal vitamin K status.

OBJECTIVE

The objective of this study was to compare, in younger and older adults, the relative bioavailability of phylloquinone from a vegetable with that of a fortified oil.

DESIGN

In a crossover design with three 15-d residency periods in a metabolic unit, younger and older men and women (n = 36) consumed a mixed diet containing 100 microg phylloquinone/d. During 2 residency periods, the mixed diet was supplemented for 5 d with either broccoli (377 microg phylloquinone/d; broccoli diet) or phylloquinone-fortified oil (417 microg/d; oil diet). The relative bioavailability of phylloquinone was defined by the difference in plasma phylloquinone, percentage serum undercarboxylated osteocalcin (%ucOC), and urinary gamma-carboxyglutamic acid in response to 5 d of supplementation.

RESULTS

For both younger and older adults, plasma phylloquinone concentrations were higher (P < 0.001) and %ucOC values were lower (P = 0.001) after the broccoli and oil diets than after the mixed diet only. Overall, the response to broccoli supplementation was not significantly different from the response to the fortified oil in either age group. Urinary gamma-carboxyglutamic acid did not change in response to supplementation.

CONCLUSIONS

There was no significant difference in the relative bioavailability of phylloquinone, as evidenced by the lack of a significant difference in plasma phylloquinone and %ucOC between the 2 groups after either the broccoli or oil diets for younger and older adults.

Assessment of phylloquinone and dihydrophylloquinone dietary intakes among a nationally representative sample of US consumers using 14-day food diaries

OBJECTIVE

To estimate dietary intakes of phylloquinone and dihydrophylloquinone in a representative sample of the American population using 14-day food diaries.

DESIGN

Vitamin K food composition data were applied to 14-day food diaries completed by a nationally representative sample of approximately 2,000 households that participated in a Market Research Corporation of America menu census survey between July 1991 and June 1992. Dietary intakes were estimated for phylloquinone and dihydrophylloquinone.

SUBJECTS

Subjects were 4,741 men, women and children with demographic characteristics similar to those of the US census population.

STATISTICAL ANALYSIS PERFORMED

Descriptive statistics and 2-sample t tests.

RESULTS

Mean reported intakes of phylloquinone among adults increased with age. Men and women in the 18- to 44-year-old groups reported mean phylloquinone intakes below the current Recommended Dietary Allowance for vitamin K. Of all study participants, 99.3% reported consumption of dihydrophylloquinone during the 14 days of diet recording; reported intakes peaked before the age of 6 years; after the age of 6 years intakes were constant.

APPLICATIONS

The Market Research Corporation of America data provide a reference range for dietary intakes of 2 forms of vitamin K in the US diet: phylloquinone and dihydrophylloquinone. Given the putative role of vitamin K in bone mineralization, low intakes of phylloquinone reported among young adults highlight the need to educate the US population about the requirement for and sources of vitamin K. The abundance of dihydrophylloquinone in the US diet suggests the need for study of its biological activity relative to phylloquinone.

Vitamin K: a practical guide to the dietary management of patients on warfarin

Warfarin has been successfully used in the medical management of thromboembolic disease for nearly six decades. It is widely assumed that a dietary vitamin K-warfarin interaction exists. To avoid this potential interference with the efficacy of warfarin in stable anticoagulation, patients typically receive instructions to consume a constant dietary intake of vitamin K. While dark, green vegetables are primary sources of dietary vitamin K, these foods are not commonly consumed on a daily basis in the United States. However, there still exists dietary resistance to warfarin that is attributable to vitamin K. Based on food analysis studies on vitamin K, it is now known that dietary vitamin K is found in certain plant oils and prepared foods containing these plant oils, such as baked goods, margarines, and salad dressings. The preparation of foods with vitamin K-rich oils may also contribute to a diet-warfarin interaction, although this has yet to be confirmed in a clinical trial. A dose-response of vitamin K on the effect of warfarin anticoagulation has not yet been established. However, there are sufficient data to suggest that a constant dietary intake of vitamin K that meets current dietary recommendations of 65-80 micrograms/day is the most acceptable practice for patients on warfarin therapy. Vitamin K composition data for commonly consumed foods are now available and may facilitate successful anticoagulation for patients being treated with warfarin.

Nutritional characteristics of wild primate foods: do the diets of our closest living relatives have lessons for us?

The widespread prevalence of diet-related health problems, particularly in highly industrialized nations, suggests that many humans are not eating in a manner compatible with their biology. Anthropoids, including all great apes, take most of their diet from plants, and there is general consensus that humans come from a strongly herbivorous ancestry. Though gut proportions differ, overall gut anatomy and the pattern of digestive kinetics of extant apes and humans are very similar. Analysis of tropical forest leaves and fruits routinely consumed by wild primates shows that many of these foods are good sources of hexoses, cellulose, hemicellulose, pectic substances, vitamin C, minerals, essential fatty acids, and protein. In general, relative to body weight, the average wild monkey or ape appears to take in far higher levels of many essential nutrients each day than the average American and such nutrients (as well as other substances) are being consumed together in their natural chemical matrix. The recommendation that Americans consume more fresh fruits and vegetables in greater variety appears well supported by data on the diets of free-ranging monkeys and apes. Such data also suggest that greater attention to features of the diet and digestive physiology of non-human primates could direct attention to important areas for future research on features of human diet and health.

Comparison of phylloquinone bioavailability from food sources or a supplement in human subjects

Phylloquinone (K) absorption was assessed in 22- to 30-y-old human subjects consuming a standard test meal [402 kcal (1682 kJ), 27% energy from fat]. The absorption of phylloquinone, measured over a 9-h period as the area under the curve (AUC), was higher (P < 0.01) after the consumption of a 500- microgram phylloquinone tablet [27.55 +/- 10.08 nmol/(L. h), n = 8] than after the ingestion of 495 microgram phylloquinone as 150 g of raw spinach [4.79 +/- 1.11 nmol/(L. h), n = 3]. Less phylloquinone (P < 0.05) was absorbed from 50 g of spinach (AUC = 2.49 +/- 1.11 nmol/(L. h) than from 150 g of spinach. Absorption of phylloquinone from fresh spinach (165 microgram K), fresh broccoli (184 microgram K) and fresh romaine lettuce (179 microgram K) did not differ. There was no difference in phylloquinone absorption from fresh or cooked broccoli or from fresh romaine lettuce consumed with a meal containing 30 or 45% energy as fat.

Tissue phylloquinone and menaquinones in rats are affected by age and gender

Phylloquinone and ten menaquinones (MK-1-MK-10) were measured in liver and eight extrahepatic tissues from male and female rats at 3, 12 and 24 mo of age. Phylloquinone and menaquinones showed characteristic tissue distribution. In liver, all 11 vitamers of vitamin K assayed were present in varying concentrations with phylloquinone and MK-6 the major forms. The only forms of vitamin K found in extrahepatic tissues were phylloquinone, MK-4 and MK-6. Brain contained only MK-4 and traces of phylloquinone. No significant gender difference was observed for phylloquinone except in heart at 3 mo of age (P </= 0.05). In heart, kidney and brain, MK-4 was significantly higher in females than in males (P </= 0.05). A similar gender effect was seen in kidney and lung for MK-6 (P </= 0.05). With age, hepatic phylloquinone and MK-6 significantly increased (P </= 0.05), whereas MK-4 was unchanged. In extrahepatic tissues, MK-4 decreased with age in heart and kidney of males and females, and in lung and cerebellum of males (P </= 0.05). MK-6 decreased with age in all extrahepatic tissued tested (P </= 0.05). The results suggest that in extrahepatic tissues, certain menaquinones may be the predominant form of vitamin K. The specific tissue distribution and the general decline of MK-4 and MK-6 in extrahepatic tissues during aging suggest a vitamin K tissue dynamic that is affected not only by diet, but also by gender, age and the specific roles of phylloquinone, MK-4 and MK-6 in metabolism. All of these factors must be taken into account in establishing the nutrient requirement for vitamin K.

Demographic, dietary and lifestyle factors differentially explain variability in serum carotenoids and fat-soluble vitamins: baseline results from the sentinel site of the Olestra Post-Marketing Surveillance Study

Biochemical measures of nutrients or other dietary constituents can be an important component of nutritional assessment and monitoring. However, accurate interpretation of the nutrient concentration is dependent on knowledge of the determinants of the body pool measured. The purpose of this study was to identify the determinants of serum carotenoid and fat-soluble vitamin concentrations in a large, community-based sample (n = 1042). Multiple linear regression analysis was used to examine effects of demographic characteristics (age, sex, race/ethnicity, education), health-related behavior (exercise, sun exposure, smoking, alcohol consumption), and intake (diet, supplements) on serum retinol, 25-hydroxyvitamin D, alpha-tocopherol, phylloquinone, and carotenoid concentrations. Age, sex, race/ethnicity, vitamin A intake, and alcohol consumption were found to be determinants of serum retinol concentration. Race/ethnicity, vitamin D intake, body mass index, smoking status, and sun exposure were determinants of serum 25-hydroxyvitamin D concentration. Determinants of serum alpha-tocopherol were age, sex, race/ethnicity, alpha-tocopherol intake, serum cholesterol, percentage of energy from fat (inversely related), supplement use, and body mass index. Age, sex, phylloquinone intake, serum triglycerides, and supplement use were determinants of serum phylloquinone concentration. Primary determinants of serum carotenoids were age, sex, race/ethnicity, carotenoid intake, serum cholesterol, alcohol consumption, body mass index, and smoking status. Overall, the demographic, dietary, and other lifestyle factors explained little of the variability in serum concentrations of retinol (R2 = 0.20), 25-hydroxyvitamin D (R2 = 0.24), and the carotenoids (R2 = 0.15-0.26); only modest amounts of the variability in serum phylloquinone concentration (R2 = 0.40); and more substantial amounts of the variability in serum alpha-tocopherol concentration (R2 = 0.62).