Vitamin K and bone health (part 2)

In our last post, we introduced the different types of vitamin K and their dietary sources, and we also noted that vitamin K has some important functions in maintaining our bone health. The question then arises: can taking vitamin K supplements protect us from osteoporosis and fractures?

Our knowledge on whether vitamin K is involved in osteoporosis comes from two types of studies — observational studies and clinical trials.

What do observational studies show?

In observational studies, researchers study the relationships between people’s behaviours and how the behaviour affects certain things. In the case of vitamin K and bone health studies for example, the ‘behaviour’ could be eating a diet that is high or low in vitamin K and seeing if there is a relationship between the diet and bone mineral density (BMD) scores or number of fractures.

To date, the majority of observational studies on vitamin K and bone health have shown that an increased risk of fractures is linked to:

  • low levels of vitamin K in the blood
  • low vitamin K1 and low vitamin K2  from diet
  • high levels of the bone protein osteocalcin in its non-functional form (osteocalcin needs vitamin K to function properly)

It is important to note however that these results may not be fully reliable. Some things to keep in mind when thinking about these results are:

  • Many things can affect a person’s diet and their food choices including their age, level of education, income, taste preferences, health consciousness, and so on. These same things can also affect a person’s bone health.
  • If a person’s diet is low in vitamin K, it is often the case that their diet is low in fruits, vegetables, cheese, and yogurt (all of which are sources of vitamin K).
  • If a person’s vitamin K levels are high, this may be an indication that they are eating an overall healthy diet that is also high in many other nutrients which are good for bone health, such as calcium, magnesium, vitamin C etc. It is also possible that they are more health conscious and do not smoke, do not drink much alcohol, and exercise more, all of which are also good for bone health.

As much as researchers try to think about all of the above scenarios and take them into account when analyzing the data from their research, it is not possible to fully control for everything and isolate only the effects of vitamin K on bone health. It may be a combination of the all of these scenarios and not necessarily the vitamin K alone that is leading to fewer fractures.

What do clinical trials show?

Clinical trials give us stronger evidence to show that one thing affects (or does not affect) another thing. This is because in clinical trials we try to control certain elements before measuring the outcome. In the case of vitamin K trials, the participants are first randomly assigned into groups. Participants in one group get a vitamin K supplement and participants in another group get  a placebo pill with no vitamin K in it. Some studies can also have more than just two groups — for example, there can be 3 groups and the participants in each group may get a different dose of vitamin K. These groups usually take their assigned pills for a number of years and at the end of the study,  the researchers compare the BMD scores and the number of fractures in the various groups. These types of clinical trials can help us single out the effects of vitamin K.

Because many clinical trials have looked at the effects of the K vitamins on bone health in different populations (women with or without osteoporosis; women taking or not taking osteoporosis medications; women of different ethnic backgrounds etc.) and in different vitamin K supplement doses, they have given conflicting results. To  get a better sense of what all the data show, the best option is to do a meta-analysis, which is a type of study which combines the results of several individual studies and provides one overall result.

In the most recent meta-analysis of clinical trials that looked at vitamin K and its effect on BMD, after taking into considerations the differences in the patient populations and differences in the way the studies were conducted, the results showed that taking vitamin K supplements has no beneficial effects on BMD.

In the case of fractures, there are a number of clinical trials that suggest that vitamin K supplements may reduce risk of fractures. However, these studies all have weaknesses, making the results inconclusive. For example, a study with positive results that is often cited by proponents of vitamin K supplementation is ‘The Vitamin K Supplementation in Postmenopausal Women with Osteopenia’ trial. This clinical trial was conducted by our research group and we found that although there were no differences in BMD, there were fewer fractures in the group of women who were taking vitamin K1 supplements compared to the women in the placebo group. But because so few study participants had fractures, the difference between the vitamin K1 group and the placebo group could have been simply by chance and not actually due to the vitamin K1 supplement.

Conclusions

What we do not know at this time is if vitamin K supplements can help reduce the risk of fractures. This is a relatively new area of research and finding real answers can take a long time. More research is definitely needed, especially clinical trials that have a large number of participants.

At present, we do NOT recommend taking vitamin K supplements to prevent osteoporosis and fractures in postmenopausal women. We recommend eating a healthy diet that is high in vegetables and fruits, has about 2-3 servings of protein, and 2 servings of dairy per day. Such diets are high in vitamin K as well as many other nutrients that are important for bone health.


Reference: Hamidi MS, Gajic-Veljanoski O, Cheung AM. Vitamin K and Bone Health. J Clin Densitom 2013;16(4):409-13. doi: 10.1016/j.jocd.2013.08.017.

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