Just wanted to share some studies and information that’s out there on Vitamin K2. It’s a bit all over the map, somewhat inconclusive but the 45 mg comes from studies out of Japan where that dose has been used therapeutically as an osteoporosis treatment since 1995.
https://pubmed.ncbi.nlm.nih.gov/18830045/
The medicinal dose used in Japan is in the form of MK4, given in 15mg doses 3x a day. (MK4 has a shorter half life than MK7 therefore it is given throughout the day)
This is the Japanese pharmaceutical:
https://www.rad-ar.or.jp/siori/english/search/result?n=444
Some potential side effects are listed. Though more studies are needed, this is where integrative practitioners are getting that dose recommendation from. I’m not suggesting that this is what individuals should be taking, just clarifying the 45 mg dosage and offering up the info to ponder. Overall, there have been mixed results on studies with vitamin K. It may be due to confounders like whether or not supplementation included calcium and vitamin D.

Here’s a great article on Vitamin K from Cleveland Clinic
https://health.clevelandclinic.org/do-you-need-vitamin-k-supplements-for-your-bone-health/
One takeaway is that there have been mixed results based upon studies but overall, inadequate vitamin K increased the risk of hip fracture. An “adequate” dose for bone health is 90 mcg for women.

This 3 year study showed improvement with a dose of 180 mcg of MK7 (the form of K2 that has a longer half life).
https://pubmed.ncbi.nlm.nih.gov/23525894/
A study that analyzed data from the large Nurses’ Health Study found that women who consumed less than 109 micrograms (mcg) of vitamin K per day were more likely to break a hip.
https://pubmed.ncbi.nlm.nih.gov/9925126/
A study of participants (both men and women) in the large Framingham Heart Study also showed a link between low vitamin K intake and increased risk of hip fractures. This study also showed an association between low dietary intake of vitamin K and low bone density in women.
https://pubmed.ncbi.nlm.nih.gov/12540415/
This article is quite thorough in its overview and analysis
https://www.naturalmedicinejournal.com/journal/vitamin-k-and-osteoporosis
So, this may be another (confusing) tool in the toolbox to address bone strength and/or density. Wish there was consensus on dosage and efficacy but apparently more studies are needed to determine that. Best to evaluate our own needs with input from our own medical support team.