Vitamin K2 supplements are widely marketed for bone health, often alongside calcium and vitamin D. The biological rationale is sound — K2 activates proteins that direct calcium into bones rather than arteries. But how strong is the clinical evidence, and do Canadians need to supplement?
Vitamin K is a fat-soluble vitamin that exists in two main forms. Vitamin K1 (phylloquinone) is found primarily in leafy green vegetables and is involved mainly in blood clotting. Vitamin K2 (menaquinone) is found in fermented foods, some animal products, and is produced in small amounts by gut bacteria. K2 is the form most relevant to bone and cardiovascular health.
Vitamin K2 itself comes in several subtypes, called MK-4 through MK-13, based on the length of their chemical side chains:
Most vitamin K2 supplements sold in Canada are either MK-4 (at pharmacological doses of 45 mg/day, the dose used in Japanese trials) or MK-7 (at nutritional/supplemental doses of 90–200 mcg/day).
Vitamin K2 acts as a co-factor (helper molecule) for an enzyme that activates specific proteins critical to bone metabolism:
Osteocalcin is a protein produced by osteoblasts (bone-building cells) that binds calcium and incorporates it into the bone matrix. Without adequate vitamin K2, osteocalcin remains in its inactive (undercarboxylated) form and cannot perform this function properly. Vitamin K2 activates the enzyme (gamma-glutamyl carboxylase) that converts undercarboxylated osteocalcin to the active form.
MGP is a vitamin K-dependent protein expressed in blood vessel walls and soft tissues. In its active (carboxylated) form, MGP inhibits calcium deposition in arteries — preventing vascular calcification. Without sufficient K2, MGP remains inactive and calcium can deposit in arteries rather than bones. This is part of the theoretical basis for the calcium-K2 connection: if you supplement with calcium, K2 may help direct that calcium to bone rather than arterial walls.
The strongest clinical trial evidence for K2 and bone health comes from Japan, where MK-4 (menaquinone-4) at doses of 45 mg/day has been approved as a prescription drug for osteoporosis since the 1990s. Multiple randomized controlled trials in Japanese postmenopausal women showed that 45 mg/day MK-4 reduced vertebral fracture incidence and maintained bone mineral density.
The challenge in applying these results to Canadian practice: 45 mg/day MK-4 is a pharmacological (drug-level) dose — about 450 times higher than the adequate intake recommendation. It's not comparable to a typical vitamin K2 supplement. Also, the Japanese diet is very low in vitamin K2 compared to North American diets, meaning the Japanese population studied may have had significant K2 deficiency. The baseline nutritional context matters.
More recent trials have examined MK-7 at supplemental doses (90–360 mcg/day), which are more relevant to what Canadians would actually take. Results are mixed:
The honest summary: there is biological plausibility and some positive trial data, but no definitive large RCT demonstrating that K2 supplementation prevents fractures in people with osteoporosis. It has not been adopted into Osteoporosis Canada's formal supplementation guidelines (which currently recommend only calcium and vitamin D).
Most Canadians get some vitamin K2 from diet, though amounts are often low:
| Food | K2 Content | Form | Availability in Canada |
|---|---|---|---|
| Natto (fermented soybeans) | ~1000 mcg per 100g | MK-7 | Asian grocery stores, some health food stores |
| Gouda / Brie cheese | ~75 mcg per 100g | MK-8, MK-9 | Widely available |
| Egg yolk | ~15–30 mcg per yolk | MK-4 | Widely available |
| Chicken (dark meat) | ~10–15 mcg per 100g | MK-4 | Widely available |
| Butter / ghee | ~15 mcg per 100g | MK-4 | Widely available |
| Liver (beef) | ~5–13 mcg per 100g | MK-4 | Widely available |
Unless you regularly eat natto (unusual in most Canadian households), it's difficult to obtain significant MK-7 from diet alone. The MK-4 amounts in Western diets are modest.
Based on the current evidence, vitamin K2 supplementation may be most relevant for:
If supplementing: MK-7 at 90–200 mcg/day is the form with the most relevant human trial data at supplemental doses. It should be taken with a fat-containing meal for optimal absorption (K2 is fat-soluble). MK-4 at 45 mg/day would replicate Japanese drug trials, but this is a pharmacological dose not available in typical supplements and not recommended without medical supervision.
K2 MK-7 supplements are widely available at Canadian health food stores (Health First, Naturopathic retailers, Goodness Me, Whole Foods Canada) and online (Amazon.ca, iHerb ships to Canada). Look for products standardized to 90–200 mcg MK-7 per capsule, ideally from certified sources. Combining K2 with vitamin D3 in a single supplement is common — verify the dose of each component.