I take K2, as I feel that together with magnesium, these are the only two nutrients of which it is very difficult to get optimal levels on an otherwise healthy paleo diet.

I take Nature's Plus 1,000 IU D3/100mcg K2, which provides 125% of K2 RDA. This is high enough to have an effect (studies show bone mineralisation starting at 15-45 mcg). Equally, to quote Stephan Guyenet from Whole Health Source, "I can't support any supplement that has more than 1 mg K2 in it. That's about the upper limit of what you can get from food. Any more than that and you're taking pharmacological doses and the long-term effects are unknown."

Nature's Plus is completely free from the usual fillers like dairy, soy, vegetable oils, gluten e.t.c. Importantly, the K2 is also in the form of MK-4, not the natto-derived MK-7 which other people have recommended. MK-4 is the "natural animal" form of K2 which mammals synthesise for themselves. (Note: humans can actually synthesise K2 from K1, but the conversion process is extremely inefficient). Each bottle also comes with a certificate of analysis from an independent lab.

K2 is a relatively novel supplement, so paying for most good quality formulations will feel like daylight robbery. I'm embarrassed to admit it, but I paid £40 for a six month supply (which I partly justified to myself as "backup D3"). I'm 2 months in and plan to review at the end and see whether it's worth continuing to supplement.

Results so far: I used to get staining on my bottom 4 front teeth. This is apparently quite common, and due to their proximity to the salivary gland, which releases highly mineralised saliva - something which was actually getting worse on nutrient dense paleo. Now, I've noticed that this is fading and I seem to be able to brush most of it away. This would definitely be consistent with K2's important role in dental health/reversal of tooth decay.

I'm taking Natural Factors K&D with 120 mcg K2 (as MK-7) and 1000 IU D3. I take 1 to 2 per day, and more D3.

As for the MK-4 versus MK-7 debate raised by Simibee, consumers choosing a K2 supplement need to be aware of a few things: Yes, MK-4 is, in theory, the "natural" form of K2 made by animals that you would find in grass fed animal products, but MK-4 in supplements is only made synthetically, in a lab. The MK-7 form is extracted from natto, in which it is naturally occurring. There is also a big difference in the dosage between these two forms. For MK-4 you need to take 45 mg per day. For MK-7 the dosage is around 120 mcg per day. You need to make sure the dose you are taking is right for the form you are taking.

Whatever you feeling is about natural versus synthetic (I'm firmly in the MK-7 camp myself), studies have shown good results with MK-4 at 45 mg/day. That means that in Canada, where the max available dose of K2 in any product is 120 mcg, an MK-4 product is useless. Taking 120 mcg of MK-4 won't get you any where.

No supplements, but I eat organ meats occasionally for MK-4 along with natto for MK-7. The natto was kind of gross at first (it has the appearance of sputum and the consistency of rubber cement) but I adapted.

I took it, but haven't for a while since I finally figured out, that my tiredness was due to low ferritin.

I used Gall Pharma Vitamin K1, 60 micrograms.

I take low dose vitamin K occasionally. My regimen is something like the following: alternate between (i) nothing, (ii) 100 mcg K1, (iii) nothing, (iv) 45 mcg mk-7 k2, (vi) nothing, and and (vii) 100 mcg mk-4 k2.

I'm not aware of a great paleo argument for taking vitamin K, provided you are eating grass-fed animal products and/or green veggies. That said, there seems to be quite a bit of good data (e.g., EPIC, ECKO) for it that is enticing....

Does anybody know of any good paleo arguments for it (i.e., why we would have had more of it in paleo times)?

I started taking Life Extension, K Complex, a few weeks ago. But I started also taking Magnesium and Potassium. I feel great lately, but not sure if it is the K, or something else, or both.

I had a bottle of Thorne Research vitamin K2. I paid $50 and used a drop, 1 mg, almost every day for a year. It helped my chapped lips a lot. I threw it out because it started to taste strange. I got the thorne research d3/k2 combo. It is a good formulation for the winter, but by summer, I will want to take K2 separately from vitamin D.

I take these sublingual tablets, but only once or twice a week because I really hate the taste of them. Once I manage to get through the bottle I will shop around for a new brand.

I bought the Thorne Pharmaceuticals K2. Paid through the teeth for it (about $40). Won't do so again. Just not worth it. Rather eat some LIVER [DELETE radicchio or lettuce] for my money.

Bullshit.

One Japanese study used mk4 at 45 mg/day. This does not mean the optimal dose is 45 mg/day. It is likely not 45 mg/day because that would be several orders of magnitude greater than can be consumed as food.