Vitamin K2 (and vitamin K)
D3+K2, MK-7, Menaquinone, Menaquinone-7, MK-4, Menatetrenone, Vitamin K1, Phylloquinone
Forms: K1 (phylloquinone, also a medicine) and K2 as MK-7 or MK-4 (menatetrenone), alone or in D3+K2 products. Vitamin D3 has its own card.
Vitamin K activates clotting proteins and calcium-binding proteins of bone and arteries; K2 (menaquinones such as MK-7) is the form added to D3. Even small amounts weaken warfarin-type blood thinners.
Legal status: Sold freely as a supplement; vitamin K1 is also a medicine for bleeding caused by warfarin-type drugs and for newborns; not prohibited in sport.
What it gives
What people use it for and what the sources report. Strength is a general category from the literature: mild, clear or strong.
Purpose
Taken with vitamin D3 'to send calcium to the bones, not the arteries', and for bone and heart health. The mechanism is plausible, but benefit in healthy people is unproven. On warfarin-type blood thinners even small amounts lowered the INR in a trial, so the doctor managing the INR must know.
What people seek and what studies show
Supplements lower blood levels of inactive matrix Gla protein, a calcification marker. In the AVADEC trial, K2 with D3 did not slow aortic valve or coronary calcification in older men; in a smaller trial in people with coronary disease, MK-7 alone slowed coronary calcification. Fewer heart events have not been shown. Data in athletes are sparse (see the note for women).
Effects
Evidence: Limited human data — some human studies, small or short
Sought effects by goal (as reported)
Possible side effects
Possible does not mean certain: whether they appear depends on dose, duration, individual response and monitoring. Below — what to watch for and how to notice it early.
1 possible side effect
level · how often it is reportedWhat the levels mean
Level: general category from the literature, not your personal risk
How often
- common
- reported often
- possible
- reported in some people
- rare
- reported occasionally
How to lower the risks
General ways to lower the chance of each side effect. No measure removes a risk completely.
Low-level side effects
Check-ups and blood tests
Which tests and check-ups to do and when. This is a guide — agree the exact schedule with a sports physician.
For women
Hard training with too little energy intake can lead to amenorrhea, low estrogen and bone loss (REDs). In 8 female elite athletes, a month of vitamin K improved bone-turnover markers in those with amenorrhea; it does not treat the cause, which needs a sports physician.
Myth & fact
“Vitamin D3 must be taken with K2, or calcium will end up in the arteries.”
The idea rests on a plausible mechanism, not on outcomes. In the AVADEC trial K2 with D3 did not slow valve or artery calcification versus placebo, and no trial has shown fewer heart events from adding K2 to D3.
Combinations
No specific combination notes for this substance yet. The stack check still adds up side effects that several substances share.
Sources
Possible side effects by body system, combinations, how to lower the risks and which tests to do — free.
Open the stack check