Disclaimer: This article is based on a school assignment where I investigated the effectiveness of vitamin D and calcium supplementation on improving bone mineral density outcomes in individuals with celiac disease. This blog post is intended to educate people, however, you should ALWAYS speak to a medical professional before starting a supplement.
If you have been diagnosed with celiac disease, you understand how important following a gluten-free diet is. Not only does following a gluten-free diet avoid the painful digestive symptoms like bloating and diarrhea, but it can also prevent a long list of potential comorbidities like metabolic bone diseases (e.g., osteoporosis).
In theory, following a strict gluten-free diet can prevent the development of nutrient deficiencies and related conditions, however, sometimes slip-ups can happen through cross-contamination or confusing food product labels.
With this thought in mind, I thought there had to be more to just following a gluten-free diet to prevent certain conditions like metabolic bone disease. Could the use of supplementation of calcium and vitamin D improve bone mineral density outcomes in people with celiac disease?
Before we jump into the research itself, we need to understand what celiac disease is and the pathophysiology that can lead to metabolic bone disease.
What is celiac disease?
Celiac disease is a common autoimmune disorder that affects up to 1% of the world’s population (1). Simply, celiac disease is when the body attacks itself in the present of a protein called gluten that is found in wheat, barley, and rye. Specifically, the body attacks these finger-like projectiles in our small intestine called villi. Villi increases the surface area for absorption in our digestive system. It makes sure our body gets the important nutrients that it needs like vitamin D and calcium. However, in individuals with celiac disease, these villi get blunted, and can no longer effectively absorb those important nutrients.
Think of your villi like a hairbrush. With long bristles or stokes, tangles and knots are caught and can be easily combed out. However, if you had a hairbrush that had shorter bristles/stokes, you may not be able to catch all the tangles and knots in your hair. This would be similar to the small intestine of someone with celiac disease.
When our body is unable to absorb nutrients, overtime this can lead to malfunctions in important processes in our body. This is why celiac disease is sometimes considered a systemic disorder as it can affect other parts of our body outside the digestive system, like our bones. In fact, it has been noted that the prevalence of low bone mineral density in individuals newly diagnosed with celiac disease can range from 38 to 72% (1).
Celiac disease and metabolic bone disease - what’s the connection?
Metabolic bone disease describes numerous disorders of bone strengths such as low bone mass, osteoporosis, secondary hyperparathyroidism, and osteomalacia, which are caused by abnormalities in bone mass, bone structure, or metabolism of calcium, phosphorus, and vitamin D (1,2).
The development of metabolic bone disease in individuals with celiac disease has been described as a multifactorial process (1).
Firstly, as described above, the absorption of essential nutrients for bone health, calcium and vitamin D, are severely compromised due to the blunting of the small intestinal villi (3). Calcium and vitamin D are often seen as “partners in crime” and need to both be available in adequate amounts to allow absorption to happen. When there is not enough vitamin D in the body, it is unable to regulate a protein called calcium binding protein, which is responsible for the absorption of calcium in our digestive tract (4). Thus, this can lead to further exacerbation of calcium deficiency.
Additionally, it is common for people with celiac disease to develop lactose intolerance, a disorder where the body is unable to digest a sugar called lactose which is found in milk and dairy products. To avoid the gas, bloating, diarrhea, and cramping that individuals experience with lactose intolerance, it is recommended that dairy products be eliminated from the diet (4). Unfortunately, milk and dairy products are often a large source in the diet of where people get their vitamin D and calcium from (5). Thus, when we cut out dairy products from our diet, our body may not get enough vitamin D and calcium that it once did (see below on non-dairy sources of vitamin D and calcium).
In celiac disease, the body’s immune system goes into overdrive and causes chronic inflammation. Normally, inflammation occurs naturally to protect the body from foreign substances like bacteria, viruses, or toxins, or from an injury. However, with celiac disease, the body mistakens gluten as a foreign substance and attacks our healthy cells in the small intestine. When these immune signals circulate our body, this leads to the activation of a whole host of bodily processes including osteoclastogenesis and bone resorption (1,2). Osteoclastogenesis and bone resorption are responsible for the breakdown of bone tissue. Thus, when the body is constantly in a chronic inflammatory state, these processes are ongoing and it can lead to bone loss (6)
Lastly, bone resorption can also occur if an individual has low calcium levels in their blood (1). Normally, bone resorption can help to maintain normal levels of calcium by breaking down bone tissue and releasing minerals, like calcium, into the bloodstream. However, if calcium deficiency is not fixed, this can come at a cost for our bone mineral density and result in bone loss (1,6).
This is all to say that A LOT is going on in the body when it comes to celiac disease and bone health, and that it is not necessarily a single phenomenon that can lead to bone loss.
So how do we go about managing AND potentially preventing metabolic bone disease in celiac disease?
Current Practice Guidelines
According to clinical practice guidelines from the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition, World Gastroenterology Organization, and American College of Gastroenterology, individuals diagnosed with celiac disease should adhere to a strict gluten-free diet that avoids all products and derivatives containing the gluten proteins from wheat, barley, and rye (7, 8, 9).
Despite the evidence linking improvement in bone mineral density in individuals with celiac disease who follow a gluten free diet, normalization of bone mineral density may not always occur due to incomplete recovery of the small intestine and or poor adherence to a gluten free diet (10, 11, 12).
In a study that examined the small intestinal lining of 465 adults newly diagnosed with celiac disease, only 8% of participants had complete recovery of their small intestinal lining after following a gluten-free diet for 16 months (10). Conversely, the majority of participants (65%) were able to achieve a state of ‘remission’ while 27% of participants were ‘non-responsive’ to the gluten-free diet with 26% experiencing no change and 1% experiencing deterioration in their small intestinal structure (10).
Adherence rates to gluten-free diets have been observed to range from 42 to 91% (11, 12). Given that even the smallest amount of ingested gluten can result in significant damage to the small intestine, this is concerning! (13) However, it must be noted that significant barriers can stand in the way of someone trying to adopt and maintain a gluten-free diet, including the learning curve of managing a new diagnosis, the cost of healthy and nutritionally acceptable gluten-free foods, and the lack of variety and cross-contamination that can sometimes occur with restaurant dining and grocery stores (11,12).
Only a limited number of international guidelines have provided recommendations in the clinical management of metabolic bone disease in celiac disease, with no recommendations for preventative action (14). Often, guidelines have outlined the importance of obtaining bone densitometry measures from individuals at diagnosis, and after one year of following a gluten-free diet; however, no guidelines have been established for ongoing routine assessment of bone health (14).
With 9-47% of individuals with celiac disease exhibiting persistent low bone mineral density after following a gluten-free diet, and more adults developing metabolic bone diseases later in life, the need for immediate and ongoing supplementation of calcium and vitamin D in individuals with celiac disease has been called into question (1).
So, is calcium and vitamin D supplementation the answer?
What the research says…
To be completely transparent, there isn’t a ton of research or recent research on this topic...which completely shocked me given the damning evidence pointing to bone health outcomes in people with celiac disease. In fact, during my research, I was only able to find four articles that fit my research question, and of the four, three of them were from the 1980s-1990s (so aspiring nutrition researchers - here is a topic of exploration for you!) (15, 16, 17, 18).
Overall, in the two studies that examined adults, neither vitamin D supplementation alone or a combination of calcium and vitamin D supplementation demonstrated additional benefits in improving bone mineral density. Although the studies observed a potential “protective effect” in the sense that participants did not have decreased bone mineral density while taking the supplements, results from these studies were not found to be statistically significant when compared to the control (17, 18). The outcomes of these studies were not completely surprising to me given that most people reach their peak bone mass around the age of 30 (19).
What did surprise me were the studies that examined children! Like the adult studies, calcium and vitamin D supplementation in children did not have additional benefits in improving bone mineral density in comparison to the control groups, and results were found to not be statistically significant (15, 16).
Although the studies did not find significant results, it is also important to look at how the studies were conducted...aka the methods! All research can be good research if it has a good methodological foundation to stand on.
Here were some of the issues I found with the studies I investigated:
1. The authors didn’t examine participants’ diets!
Although supplementation of vitamin D and calcium were the stars of the show, it is important that researchers also looked at the participants’ diet. Unfortunately, the majority of the studies failed to look at participants’ dietary consumption of calcium and vitamin D. This is huge and makes it difficult to infer whether the supplements actually had an effect on participants’ bone health outcomes.
2. Adherence to supplements
Again, the majority of the studies did not examine participants’ adherence to taking the vitamin D and calcium supplements, making it difficult to conclude whether the supplements (or the person’s diet) had an effect on bone health. Only one study recorded adherence of participants’ vitamin D and calcium supplementation, and although adherence was high during the first year of the study (84%), it took a small dip during the second year (74%) (16).
3. Control groups
When it comes to research studies, you want to make sure that the control group is similar to that of the research group so that you can better conclude that the treatment, in this case vitamin D and calcium supplements, had an effect on participants rather than some other confounding factor. Unfortunately, this was not always the case in some of the studies. For example, in one study that examined children, the control group consisted of healthy children who did not have a celiac disease diagnosis. Evidently, the control group had by far better bone health outcomes than the children with celiac disease, making it difficult to know whether the children with celiac disease benefitted from the supplements or not (16). Additionally, in another study that looked at adults, the control group had more participants who were either vitamin D insufficient or vitamin D deficient at the beginning of the study (15). Thus, the experimental group already had a leg up from the control group - so was it supplements that resulted in a better outcome, or the fact that less participants in the experimental group were not deficient?
In creating practice guidelines, the more studies with consistent types and amount of supplement dosages, the easier it is to gather evidence to formulate a recommendation. However, with the limited studies on this topic and the different types and amount of vitamin D and calcium supplements used in each study, it is difficult to make, if any, recommendation. From very low doses to moderately high - we cannot conclude anything at this moment. As the infamous research line goes, “more research is needed in this area”.
5. Small sample sizes and short term studies
Ideally, larger sample sizes that are observed over a greater period of time provide more reliable results with better precision and power (20). In the studies examined, the sample sizes were relatively small from 14 to 30 participants with the longest study following participants up to 24 months. Thus, we really don’t know what the long-term effects of consistent supplementation of calcium and vitamin D in individuals with celiac disease looks like.
Although this may all sound like bad news, it is a start! Hopefully in the near future, more research will be able to inform practice guidelines in the prevention and management of metabolic bone disease in individuals with celiac disease.
So what can we do in the meantime?
Tips to Keeping Your Bones Healthy
Although taking vitamin D and calcium supplements can benefit your intake (just make sure you first speak to a medical professional before starting), there are other ways you can help keep your bones healthy and prevent or slow down bone loss.
1. Follow a diet that includes plenty of foods that contain calcium!
For adults 19-50 years of age, the recommended dietary allowance of calcium is 1,000mg per day. For women over the age of 50 and men over the age of 70, this increases to 1,300mg per day (19).
Although dairy products like milk, cheese, and yogurt, are often associated as being high sources of calcium, there are many other foods that contain calcium, such as almonds, broccoli, kale, canned salmon with bones, sardines, and soy products like soy beverages, tofu, and edamame (19).
2. Don’t forget calcium’s partner-in-crime, vitamin D!
Vitamin D is another vital nutrient for healthy bones that can be obtained in our diet and from the sun. For adults ages 19-50 years, it is recommended that they consume 600 international units (IU) per day, and 800 IU per day after the age of 71 (19, 21).
Common food sources of vitamin D include oily fish like salmon and trout, and fortified products like dairy, soy beverages, eggs, and sometimes orange juice! Although we can also obtain vitamin D through the sun, if you live in the Northern hemisphere, it may not be enough. Speak with your doctor or medical professional about vitamin D supplements during the winter months! (21)
3. Include weight bearing and resistance exercises into your regular physical activity
Like muscle, bone is living tissue that needs regular physical activity to grow and build stronger. Include weight bearing activities such as hiking, running, dancing, or climbing stairs, that force you to work against gravity. Resistance exercises - like lifting weights - can also help to build stronger bones. (22)
4. Limit your alcohol consumption and quit smoking
Heavy alcohol consumption can lead to bone loss, increased risk of fractures, and deficient bone repair (19, 23). It is recommended that to prevent osteoporosis, women should drink no more than one alcoholic drink per day and men should drink no more than two alcoholic drinks per day (19).
Although we tend to associate smoking with cardiovascular diseases and lung damage, smoking can also wreak havoc on your bones! Specifically, smoking can lead to a decrease in blood flow to your bones, slow down the production of bone producing cells, decrease the body’s ability to absorb calcium, and affect the balance of certain hormones like estrogen which helps build and maintain bone structure in both men and women (24).
Speak with your doctor, create a plan, and seek out support if you intend to reduce your alcohol consumption and or quit smoking.
There isn’t enough research to conclude whether vitamin D and calcium supplementation has an effect on improving bone mineral density outcomes in people with celiac disease. Furthermore, there isn’t enough CONSISTENT evidence to recommend a certain type and amount of vitamin D and calcium supplement for celiac disease at this moment.
Although research is lacking, there are diet, physical activity, and lifestyle factors that can prevent further bone loss.
If you are thinking about taking vitamin D and or calcium supplement, it is important to speak with your doctor or a medical professional.