Vitamin K2

Choosing K2 is mostly about choosing the right menaquinone. These are the questions our naturopaths ask in store.

A good fit if

• You're past menopause and want to look after your bones. That's where nearly all the K2 research has been done
• You want MK-7 specifically, at 90 to 180 µg a day, the range that has both research behind it and is legal in Australia
• You already take vitamin D and want the partner it's most often studied with
• You eat almost no fermented food, so you're not getting any from natto or fermented cheese

Check with us first if

• You have a condition that affects how you absorb fat, such as Crohn's disease, cystic fibrosis or cholestasis. Vitamin K needs fat from your food to be carried, and in one study of people with Crohn's in remission, 47 per cent of their osteocalcin hadn't been switched on.
• You're on dialysis or have advanced chronic kidney disease. Low vitamin K is very common there, the supplement trials have had mixed results, and it's a conversation for your kidney specialist team.
• You're pregnant or breastfeeding. The Adequate Intake stays at 60 µg a day, but no trial has tested supplement doses in pregnancy or breastfeeding, so we can't reassure you about them.
• It's for a child. The legal limit is 90 µg a day for ages 10 to 18 and 45 µg for under-10s, and the only trial in children used 45 µg for eight weeks.
• You're a man buying it for your bones. The one trial that tested both men and women found the benefit in women past menopause and no effect in men.
• You eat natto or lots of greens and the amount you eat changes a lot. Keeping your intake steady matters more than how much you get.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before starting.

• Vitamin K2 as MK-7 (menaquinone-7). Best known for: The long-chain menaquinone from natto, and the form nearly every Australian K2 product is built on. Absorption: Measured head to head against MK-4 and won outright: a single 420 µg dose peaked in serum at six hours and was still detectable 48 hours later, and 60 µg a day for a week raised serum MK-7 in every subject. A fortified yoghurt delivered more than a soft-gel capsule of the same amount. Typical use: Bone maintenance in postmenopausal women, where the long trials are genuinely split rather than uniformly positive. Schedule 1 item 3252, permitted with conditions, oral use only.
• Vitamin K2 as MK-4 (menatetrenone). Best known for: The short-chain menaquinone behind the Japanese bone research, where it was a 45 mg a day prescription drug rather than a supplement. Absorption: The finding that settles it: at a 420 µg single dose, MK-4 wasn't detectable in the serum of any subject at any time point, and 60 µg a day for a week didn't raise serum MK-4 either. Typical use: Its half-life runs to a few hours, which is why the Japanese protocol splits the dose three ways through the day. It's absent from Schedule 1, so it can't be an active ingredient in an Australian listed medicine.
• "Vitamin K2" with no menaquinone named. Best known for: A label that tells you the family and nothing else. K2 runs from MK-4 through MK-13, and they don't behave alike. Absorption: Varies enormously by sub-form, which is exactly why the bare name isn't enough information to buy on. Typical use: "Vitamin K2" isn't a Schedule 1 name in its own right. A compliant Australian product names the menaquinone it contains, and in practice that's almost always MK-7.

Reference values. There's no reference value for K2 on its own. The NHMRC and NZ Ministry of Health set an Adequate Intake for vitamin K as a whole rather than an RDI, because the evidence wasn't strong enough for one. It's 60 µg a day for women 19 and over, 70 µg for men, and 60 µg through pregnancy and breastfeeding. Children need 25 µg at ages 1–3, 35 µg at 4–8, 45 µg at 9–13 and 55 µg at 14–18.

Typical supplemental range. Australian MK-7 products usually give you 60 to 180 µg a day, and the top of that range is the legal limit, not a recommendation. The research within it is limited but real: 90 µg a day slowed bone loss at the hip (the femoral neck) in women past menopause over a year, and 180 µg a day was the dose in the longest positive MK-7 trial. Much of the other research used 360, 375 or 720 µg, more than can be sold here, so treat those numbers as research findings, not as a dose to take.

Upper level. No upper level has been set. In the NHMRC's own words: "No adverse effects have been associated with vitamin K consumption as food or supplements in humans or animals, so it is not possible to set a UL." That doesn't mean there's no limit at all. Australian law separately caps how much MK-7 a listed medicine can give you, and it's that legal cap, not the nutrition reference, that decides what's on the shelf.

Worth knowing. Take it with a meal that has some fat in it. Vitamin K is fat-soluble and travels on the fat-carrying particles in your blood, which is why levels peak about six hours after a fatty meal. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Natto (fermented soybeans), 85 g: 850 µg of vitamin K, mostly as MK-7: realistically the only common food that's a serious K2 source
• Soybeans, roasted, ½ cup: 43 µg
• Fermented cheeses, Jarlsberg among them: no figure in the reference tables we use, but K2 status improved in one study on Jarlsberg
• Green leafy vegetables: spinach, kale, broccoli: 110 to 145 µg a serve, but that's K1 rather than K2

This list is the part of the page we will not shorten. If any of it applies to you, talk to one of our naturopaths or your doctor before starting.

• Anyone on warfarin or another vitamin K antagonist. Direct, clinically significant interaction; prescriber-managed, never advised from retail.
• Anyone eating natto while on warfarin. Published advice is that normal natto must be avoided.
• Anyone on any oral anticoagulant. The food interaction is treated as clinically relevant by class.
• Pregnancy. Adequate Intake is unchanged at 60 µg a day, but no supplemental-dose trial exists; refer, do not reassure.
• Breastfeeding. Same position as pregnancy; no supplemental-dose evidence found.
• Children. MK-7 is legally capped at 90 µg daily for ages 10–18 and 45 µg for under-10s.
• Fat malabsorption conditions (Crohn's, cystic fibrosis, cholestasis). Functional shortfall is common; refer for assessment.
• Dialysis and advanced chronic kidney disease. High deficiency prevalence, inconsistent outcomes; practitioner territory.
• Men buying for bone. The only trial to test both sexes found no effect in men.
• Long-term K2 tolerability. One meta-analysis found adverse reactions no different from control, another found them higher (RR 1.33) with no serious events, largely in MK-4 trials at 45 mg.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before starting.