Diet for Kidney Stones Prevention

Diet and Kidney Stone Prevetion
Click image to download handout.

Many of the UHN Osteoporosis Program patients ask our doctors: “Doctor, I am prone to kidney stones. I know I need calcium for my bone health, but I have heard that taking calcium supplements is bad for kidney stones. What should I do?” Some patients are also asking our doctors about foods high in oxalates, which are also bad for kidney stones.

So, the UHN Osteoporosis Program’s nutrition and patient education experts have put together a handy handout for people who are prone to kidney stones and are thinking about changing their diet to help prevent them.

This handout includes a brief description of:

  • What are kidney stones and who is prone to them
  • Dietary tips to help prevent kidney stones, while maintaining your bone health
  • Top foods to HAVE and to AVOID to help prevent kidney stones

We hope that you enjoy reading this handout and find it informative. If you have any feedback, please don’t hesitate to leave a comment. If you would like us to talk about specific topics, please leave us a comment here or on our twitter or facebook.

By Dr Maryam S. Hamidi and Dr Luba Slatkovska

Calcium supplements

Many of our research and clinic patients have questions about calcium supplements, such as which form of calcium supplements to take and how much, and how to avoid common side effects such as constipation.

Our nutrition researcher, Dr. Maryam S. Hamidi, answers these questions and offers other helpful information in the video below:

You can find the our calcium calculator, the Calcium Assessment Tool here.


Upper body exercises

In follow up to our previous post from yesterday, certified exercise specialist Dr. Marta Erlandson begins our series of exercise videos by demonstrating upper body exercises that are good for developing bone and muscle strength.

Exercise for bone health

As we have highlighted previously, exercise is important in both preventing and treating osteoporosis. But physical activity can be a confusing issue for osteoporosis patients and individuals with low bone mass as some types of exercises can harm weakened bones.

The Osteoporosis Exercise Guide gives detailed descriptions of bone-friendly exercises and also describes what types of exercises and activities can be harmful to bone health. We have also recently created a few videos with Dr. Marta Erlandson PhD, an exercise expert, and former post doctoral fellow with the Osteoporosis Program. Marta is a Certified Exercise Physiologist and recently appointed Assistant Professor at University of Saskatchewan, College of Kinesiology.

In her first video, Marta talks about exercise and bone health and what kind of movements to avoid if you have osteoporosis.

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.


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.

Vitamin K and bone health (part 1)

The idea of using nutritional supplements to prevent diseases has been gaining currency over the past several years. For osteoporosis, vitamin K has been getting a lot of attention because of its role in bone health. But can vitamin K supplements actually prevent osteoporosis? In a review article published recently in the Journal of Clinical Densitometry, our nutrition expert, Dr. Maryam S. Hamidi along with Dr. Gajic-Veljanoski, our clinical epidemiologist, and Dr. Cheung , a professor of medicine and the director of our program, survey the existing research literature on vitamin K and its effects on bone health. 

Background on vitamin K

vitamin KVitamin K is a fat-soluble vitamin that plays different roles in our bodies but  is mostly known for its role in blood coagulation.*

Vitamin K is not just one substance. It represents a group of compounds that are chemically very similar. There are two main forms of vitamin K — vitamin K1 and vitamin K2. Vitamin K1 is made by plants and is also the form of vitamin K that is most present in our diets. The main sources of vitamin K1 include green leafy vegetables, broccoli, brussel sprouts, avacado, kiwi, green grapes, some herbs, and green and herbal teas. Vitamin K2 further represents many different forms of vitamin K, known as menaquinones (MK-n). MK-4 to MK-10 are  the main forms of vitamin K2 that we get in our diet from foods from animal sources or fermented products.  Dietary sources of MK-4 include fish, eggs, liver, kidney, milk, butter, and fermented cheese or vegetables. Although vitamin K1 is the form we ingest mostly, MK-4 is the form of vitamin K that is most present in our bodies, leading some researchers propose that vitamin K1 is being converted in our bodies to MK-4.

Vitamin K and bone function

Vitamin K is involved in three broad areas of bone health:

  • vitamin K helps calcium get into bone
  • vitamin K is required for osteocalcin, an important bone protein, to function during bone formation
  • vitamin K may also be involved in maintaining bone strength

Research on vitamin K, bone density, and fractures

Our knowledge on how vitamin K affects bone health comes from two types of studies — observational studies and clinical trials. In part 2, we will summarize the latest research on vitamin K and osteoporosis and whether current research supports the idea of taking vitamin K supplements for osteoporosis prevention.

*Contrary to general belief, getting too much vitamin K from diet does not cause blood clots in healthy people who are not taking blood thinning medications. That said, vitamin K reduces the effectiveness of blood thinning medications and people who take such medications should monitor their intakes of vitamin K to avoid blood clotting complications.

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.

Meeting your calcium needs from food vs supplements

We spoke to Dr. Maryam S Hamidi, our nutrition researcher, about the controversy around calcium supplements and why it is better to get your calcium from food. Dr. Hamidi also advised us on the best foods to eat when trying to meet our daily calcium needs.

A little more about Dr. Hamidi: She completed her PhD in June 2012 under the guidance of our Program Director and osteoporosis and women’s health expert, Dr. Angela M. Cheung. Dr. Hamidi’s graduate research explored the relationships between diet and bone health. After obtaining her PhD, Dr. Hamidi continued to work with the Osteoporosis Program as a Scientific Associate. She keeps busy doing even more research on diet and bone health and overseeing research studies in fracture patients. You can connect with her on her facebook page or via twitter.