Introduction

Coeliac disease is an autoimmune condition triggered by the consumption of gluten.  When people with coeliac disease consume gluten the immune system attacks the small intestine, causing damage to the gut. This damage can impair the body’s ability to absorb nutrients, resulting in nutrient deficiencies. Understanding these deficiencies is important for patient care as supplementation may be required for patients with the disease. This article aims to address the most common deficiencies associated with coeliac disease, why they arise and what can be done to treat them.

Understanding coeliac disease

Coeliac disease is an autoimmune condition in which the body’s own immune system attacks its tissues when you eat gluten.¹ Gluten is a name for proteins that are found in wheat, barley, and rye, as well as oats and triticale.

It is a disease strongly associated with genetic markers which play an important role in immune system function. These genetic markers predispose individuals to developing coeliac disease when exposed to gluten, which triggers an abnormal immune response.

During an immune response in coeliac patients who have ingested gluten, gluten-derived peptides interact with an enzyme that modifies the gluten proteins. These modified proteins are recognised as foreign by the immune system, triggering an immune response, and resulting in inflammation of the small intestine. This causes damage to the villi, the finger-like projections that are responsible for nutrient absorption in the small intestine. When damaged, the small intestine lining becomes flattened, which reduces the surface area available for nutrient absorption.

Damage to the small intestine impairs the absorption of nutrients including vitamins, minerals and macronutrients, including carbohydrates, protein and fats: nutrient deficiencies arise from this impaired absorption.

Coeliac disease also has further systemic implications, including skin manifestations, osteoporosis, infertility, and neurological complications.²

Common vitamin deficiencies associated with coeliac disease 

Due to this intestinal damage associated with gluten consumption, vitamin deficiencies are common in coeliac disease.³ The extent of these deficiencies may be affected by the severity of intestinal damage. Treatment for these deficiencies is important in patients with coeliac disease, however, this should be following advice from a healthcare professional. Common vitamin deficiencies in coeliac disease include:

Vitamin D

Vitamin D is important for the absorption of calcium and is necessary both for bone health and general well-being. It is a vitamin that is made by the skin in response to sunlight. Factors contributing to vitamin D deficiency in coeliac disease include:

• Malabsorption – due to damage to the small intestine
• Decreased sunlight exposure – decreased outdoor activity due to symptoms may affect sun exposure
• Secondary hyperparathyroidism – low serum calcium can cause elevated parathyroid hormone, contributing to osteoporosis (abnormally low bone mass and bone mineral density)
• Inflammatory state – inflammation in the small intestine interferes with vitamin D metabolism
• Dietary factors – limitations in dietary intake and variety due to dietary restrictions or personal  preference  

For the general population, 700mg of vitamin D is recommended daily. However, adults with coeliac disease are recommended to consume at least 1000mg of vitamin D. This may vary depending on factors such as age, dietary intake and comorbidities and some individuals may require supplementation to correct the deficiency however, this will be managed on a case-by-case basis.

Vitamin B12⁴

Deficiencies in vitamin B12 cause symptoms such as fatigue, anaemia, and neurological problems, therefore, it is very important for individuals with coeliac disease to be regularly monitored for vitamin B12 deficiencies. A vitamin B12 deficiency may be caused by:

• Malabsorption – due to damage to the small intestine
• Production of intrinsic factor – this is a protein that binds to vitamin B12 to allow for its absorption. Gastritis, a gastrointestinal disorder associated with coeliac disease, can reduce the production of intrinsic factor
• Pernicious anaemia – a type of anaemia caused by vitamin B12 deficiency
• Dietary restrictions – vitamin B12 consumption may be limited by dietary restriction or personal preference
• Secondary causes – other gastrointestinal conditions, such as bacterial overgrowth (e.g. small intestinal bacterial overgrowth - SIBO) or chronic inflammation may lead to poorer absorption of B12    

Treatment for vitamin B12 deficiency may involve injections or oral supplementation.⁴ Furthermore, addressing any other gastrointestinal issues can help to improve nutrient absorption.

Folate (vitamin B9)

People with folate deficiency experience symptoms such as weakness, irritability, headaches, difficulty concentrating and fatigue. It is especially concerning for pregnant people. Deficiencies in folate in people with celiac disease may occur due to:

• Malabsorption – damage to the small intestine  
• Inflammation – inflammatory processes can affect intestinal function and transport mechanisms of vitamins
• Dietary restrictions – dietary restrictions or personal preference may affect how much folate is consumed in the diet
• Secondary causes - such as autoimmune disorders and bacterial overgrowth

Treatment for folate deficiency includes a change in diet, oral supplementation, or injections.⁴

Iron

Iron deficiency is common in coeliac disease, with the primary cause being gastrointestinal bleeding. Other causes include:

• Malabsorption – due to alterations in the small intestine
• Gastrointestinal bleeding – chronic inflammation can lead to bleeding, resulting in iron loss in poo
• Dietary factors – dietary restrictions and personal preference may mean that iron-rich foods are limited, whilst gluten-free products may be lower in iron than their gluten-free counterparts
• Increased iron requirements - caused by menstruation, pregnancy, lactation or growth spurts

Deficiencies in iron can lead to symptoms such as weakness, fatigue, shortness of breath and cold intolerance. In more severe cases, iron deficiency anaemia can develop.

Vitamin K

Vitamin K is important for bone health, blood clotting and cardiovascular health. It can occur in people with coeliac disease due to:

• Malabsorption – primary absorption of vitamin K occurs in the small intestine
• Bile production – absorption of vitamin K depends on bile production and secretion, which can be impaired in people with celiac disease
• Gut microbiota changes – an imbalance of the gut microbiota can affect the synthesis of vitamin K as bacteria in the colon can make vitamin K
• Dietary factors – such as dietary restrictions or personal preference 
• Medication – some medications used in coeliac disease can affect bile production, which affects vitamin K absorption

Deficiencies in vitamin K can result in cardiovascular disease, osteoporosis, and bleeding disorders.

Clinical implications and diagnostic considerations

Importance of screening for vitamin deficiencies in coeliac disease

Screening for vitamin deficiencies in coeliac disease is important as it is important in the detection and prevention of complications of vitamin deficiencies, monitoring responses to treatment and allowing for an individualised approach to treatment.

Screening for vitamin deficiencies is an important part of monitoring in coeliac patients and is important in the early detection of deficiencies. As deficiencies can lead to complications, early detection through screening contributes to improving long-term health outcomes.

Furthermore, screening ensures that patients are managing their nutritional health well on a gluten-free diet and getting all the essential nutrients. As a monitoring tool, screening provides a baseline for monitoring nutritional status in comparison to that at the time of diagnosis to analyse adherence and effectiveness of treatment.

Amongst patients with coeliac disease, vitamin deficiencies vary based on factors such as disease severity, diet, age, and other illnesses. Therefore, screening can provide treatment strategies based on each individual patient.

Diagnostic tests for assessing nutritional status in coeliac disease

As screening is important in the diagnosis, treatment and management of coeliac disease, there are numerous diagnostic tests in place which allow healthcare providers to assess nutritional stats. These include:

Blood tests

There are numerous blood tests used to test for nutrient deficiencies in coeliac disease:

• Complete blood count: to help detect anaemia and vitamin deficiencies
• Iron studies: to check for iron deficiency
• Vitamin levels: to check levels of vitamins such as B12, folate and vitamin D
• Calcium levels: to assess bone health and calcium absorption
• Albumin and prealbumin: these are protein markers that indicate malnutrition or a protein deficiency
• Electrolyte panel: to assess levels of potassium, magnesium, and other electrolytes

Serological tests

This test is used to check for the presence of anti-tissue transglutaminase antibodies (anti-tTG) and anti-endomysial antibodies (EMA). The presence of these enzymes may indicate malabsorption and nutrient deficiencies.

Intestinal biopsy

This is a technique commonly used in diagnosis. It can provide insight into how effectively the small intestine can absorb nutrients.

Nutritional assessment by a dietician

Dieticians may conduct a nutritional assessment providing patients with individual dietary recommendations having evaluated their dietary intake and nutrient deficiencies.

Management strategies

Coeliac disease must be strictly managed to maintain optimum health. These management strategies include:

Following a gluten-free diet

This is very important in coeliac patients. This involves eliminating all sources of gluten from the diet and being aware of avoiding hidden sources of gluten. Patients will likely receive guidance from a healthcare professional on how to implement a gluten-free diet.

Patient education

 This could include education on what foods will provide the most nutrients and give patients the best chance of not suffering from nutrient deficiencies. Eating naturally gluten-free foods such as fruits, vegetables, gluten-free grains (rice and quinoa) and lean proteins can help.

Nutritional support

Any nutrient deficiencies in coeliac disease should be identified, monitored, and treated through either dietary changes or supplementation.

Patient support

Patients should be fully informed about dietary management, the importance of dietary adherence and the potential complications of coeliac disease. Patients should have access to all information about the disease and access to other resources such as support groups.

Preventing cross-contamination

Cross-contamination of gluten can negatively affect coeliac patients, therefore, be aware of this when cooking and dining out

Regular monitoring for complications

Many complications can arise in coeliac patients, and these must be monitored and treated accordingly.

Summary

To conclude, nutrient deficiency is very common in patients with coeliac disease, due to intestinal damage and decreased nutrient absorption. Regular monitoring and screening for vitamin deficiencies is important in the management of patients with coeliac disease, to ensure that new deficiencies have not developed or that known deficiencies are being managed effectively. Nutrient deficiencies in coeliac disease can primarily be managed by adhering strictly to a gluten-free diet and ensuring that enough foods containing essential nutrients are consumed. In some cases, supplementation may be required to manage symptoms and optimise health outcomes. Collaboration between healthcare providers, including, dieticians, primary care physicians and gastroenterologists, ensures that comprehensive care is provided and that nutrient deficiencies are effectively managed in each individual case.