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ZenBodyLove

Vitamin K2

Vitamin K2 (menaquinones, including MK-7 from the fermented soybean food natto) supports the carboxylation of vitamin K-dependent proteins such as osteocalcin, and supplementation trials consistently shift these markers. Effects on outcomes that matter are less certain: pooled trials in postmenopausal women show small lumbar spine bone density gains that shrink when higher-risk-of-bias trials are removed, fracture results are inconsistent, and effects on artery calcification and stiffness are mixed. MK-7 supplements can weaken the effect of vitamin K antagonist anticoagulants even at low intakes.

  • Longevity
  • Vegan

Evidence retrieved up to

What the research shows

In postmenopausal women, trials of vitamin K supplementation, including vitamin K2, give inconsistent results on fractures: one meta-analysis found fewer clinical fractures but judged the evidence insufficient, and another found no overall difference.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsUnclear

Who this is about

postmenopausal women

Practical note

Graded low: randomised trials, downgraded for risk of bias (the effect lost significance in low-risk-of-bias trials) and inconsistency (the 2022 pooled estimate only reached significance after one heterogeneous study was excluded).

Sources

Pooled trials in postmenopausal women found small gains in lumbar spine bone mineral density with vitamin K2 supplementation, but in a wider vitamin K meta-analysis the gains became smaller and not statistically significant when trials at high risk of bias were removed.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsUnclear

Who this is about

postmenopausal women

Practical note

Graded low: randomised trials, downgraded for risk of bias (the effect shrinks in low-risk-of-bias trials) and inconsistency between meta-analyses. Many trials combined vitamin K2 with other treatments.

Safety note

A 2022 meta-analysis of 16 trials found no difference in adverse reactions between vitamin K2 and control groups.

Sources

In adults taking vitamin K antagonist anticoagulants, MK-7 supplements at intakes below the usual retail dose lowered the anticoagulant effect in some people in a dose-response study.

Low certaintyFurther research is likely to change this.
Caution: see the safety noteRisk

Who this is about

adults taking vitamin K antagonist anticoagulants

Practical note

Graded low: a single small uncontrolled dose-escalation study in 15 healthy volunteers given acenocoumarol (indirect population, imprecision), though the effect was large and dose-related. The study tested daily MK-7 intakes of 10, 20 and 45 micrograms.

Vegan note

Natto is a concentrated plant source of MK-7; the study tested supplements, not foods.

Safety note

The study authors concluded that MK-7 supplements should be avoided by people on vitamin K antagonist therapy; decisions about medicines and supplements belong with the prescribing clinician. A systematic review of dietary vitamin K suggested keeping intake stable rather than restricting it.

Sources

Among Japanese adults, people who habitually eat natto, a fermented soybean food that is the richest natural source of vitamin K2 as MK-7, have markedly higher serum MK-7 than people who eat little or none.

Moderate certaintyFurther research may change the size of the effect.
No known concerns at usual amountsBenefit

Who this is about

Japanese adults

Practical note

Graded moderate for serum MK-7 (observational studies, upgraded for a large effect), matching the GRADE rating given in the review; the osteocalcin and bone density associations were rated low to very low and are limited to Japanese populations.

Vegan note

Natto is a fermented soybean food, so it is a plant-based source of vitamin K2 for people following a vegan diet.

Safety note

Natto is a concentrated source of MK-7; see the anticoagulant claim in this topic.

Sources

In randomised trials of middle-aged and older adults, including postmenopausal women, vitamin K2 or vitamin K supplementation consistently lowered undercarboxylated osteocalcin, a marker of low vitamin K status in bone.

Moderate certaintyFurther research may change the size of the effect.
No known concerns at usual amountsBenefit

Who this is about

middle-aged and older adults, including postmenopausal women

Practical note

Graded moderate: consistent direction across meta-analyses of randomised trials, downgraded one level for indirectness because a biomarker shift does not by itself show a change in bone strength or fractures.

Sources

In adults, controlled trials of vitamin K supplementation, including vitamin K2, show inconsistent effects on artery calcification and no clear effect on arterial stiffness.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsUnclear

Who this is about

adults

Practical note

Graded low: surrogate outcomes only (indirectness), few small trials with substantial heterogeneity (inconsistency, imprecision). A 2019 meta-analysis of 13 trials reported a pooled reduction in calcification; a 2020 systematic review of nine trials judged the effect inconsistent.

Sources