Which form of vitamin K2 is better: MK-4 or MK-7?
MK-7 is actually absorbed into the blood at normal supplementation doses, whereas MK-4 does not rise measurably at that dose. If you take vitamin K2, choose a supplement that lists MK-7 (menaquinone-7) on the label.
MK-7 is the better choice when taking vitamin K2. After a dose of 420 µg, MK-4 could not be detected in the blood at any measurement point. MK-7 reached a measurable peak at the same dose after six hours and was still present 48 hours later. After seven days of 60 µg daily, blood levels rose in all participants with MK-7 only. On the label, look for 'vitamin K2 as menaquinone-7' or the abbreviation MK-7, with the dosage in mcg. The mention of MK-4 or menatetrenone can be ignored if you want the supplement to actually reach your bloodstream.
That difference in absorption has consequences. Only MK-7 activates proteins outside the liver at a normal supplementation dose, including proteins involved in bone formation and the protection of blood vessel walls. MK-4 and vitamin K1 fall short at the recommended daily intake level. A portion of the MK-7 you take is converted in the body to MK-4, so both forms ultimately play a role.
For bone density in postmenopausal women, discuss it with your doctor. In research, women received 180 mcg of MK-7 per day for at least one to three years. Studies show a positive effect on bone mineral density, but whether it also prevents fractures is not yet certain enough for a routine recommendation. Randomised studies did not show a consistent effect on the most commonly measured sites in the skeleton, and the studies that looked at fractures have methodological limitations.
The same applies to rheumatoid arthritis: this is something to discuss with your doctor. In one study (42 participants per group), people with rheumatoid arthritis received 100 mcg of MK-7 per day as a supplement to their regular medication for three months, after which inflammatory markers decreased. That is interesting, but too early for firm conclusions. For cardiovascular health and cholesterol, the evidence is too thin: too little has been studied to make a recommendation. Your money is not well spent there.
All claims are based on one to a few studies per outcome. The absorption data come from one comparative study (PMID 23140417, confirmed by PMID 39091191). Bone effects are supported by mechanistic-clinical studies (PMID 32244313) and a systematic review in postmenopausal women (PMID 24090644). The RA data come from one small RCT (PMID 26073022).
Should you take vitamin D together with vitamin K2?
For osteoporosis, there is reasonable evidence that vitamin K2 and D3 together do more for bone density than either one alone; for healthy people without bone problems, the necessity of the combination has not been demonstrated. Do not use vitamin K with blood thinners, and always discuss high vitamin D doses with your doctor.
Does vitamin K2 help your bones and blood vessels?
For bones in postmenopausal women the evidence is reasonably strong; the combination with vitamin D gives the greatest effect. For blood vessels the indications are interesting, but hard evidence from completed studies is still lacking.
What is the optimal vitamin D level?
For bone health, 50 nmol/l is the most widely accepted target level, achievable with 800 IU of vitamin D per day. Whether a higher level also provides benefit beyond the skeleton has not been demonstrated.
Does vitamin D prevent me from breaking bones?
Vitamin D alone does not demonstrably reduce the risk of bone fractures. When combined with calcium it does help, particularly in older adults and people with a deficiency.
How do I know whether I have enough vitamin D, and should I be supplementing?
A blood test (25-hydroxyvitamin D) tells you whether you have a deficiency. At a value below 20 ng/mL, supplementing is worthwhile, particularly for your bones. For your heart, vitamin D has no proven effect.
Do calcium and vitamin D supplements really help against bone loss?
Calcium and vitamin D together can improve bone density and slightly reduce the risk of hip fractures when a deficiency has been demonstrated. Vitamin D as a standalone supplement does little if your blood levels are already adequate.