• Alyssa Fontaine, RD
• Apr 28, 2026

Hidden Nutritional Risks of Long-Term Vegan Diets (and How Dietitians Address Them)

Believe it or not, although vegan diets are widely recognized for their health benefits, they can also carry hidden risks over time.

Certain symptoms related to nutrient deficiencies may develop gradually and go unnoticed for years. That’s why early awareness is essential, prevention is far easier than treatment.

A well-planned vegan diet, developed with the guidance of a registered vegan dietitian, can provide a personalized approach that removes uncertainty and supports long-term health.

Why Do Problems Appear Years Later Rather Than Within Months?

Vitamin B12

One reason vitamin B12 deficiency symptoms may take years to appear is that the body is an efficient recycler. It can recover and reuse stored vitamin B12.

Some individuals may experience no symptoms for months — or even years — despite consuming little to no B12.

However, recycling cannot continue indefinitely. Regular B12 supplementation is essential to prevent deficiency, which can lead to irreversible neurological damage if left untreated.

Iron

A similar process occurs with iron. The body recycles iron during the normal turnover of red blood cells. Old cells are broken down so new ones can be produced.

This recycling process is not perfectly efficient, and small amounts of iron are lost over time. These losses must be replaced through diet or supplementation.

Iron, Vitamin B12, and Iodine: What Lab Tests Really Reveal

Iron

Blood tests can assess iron status, but interpreting results requires examining several markers:

• Hemoglobin: Indicates how much iron is present in red blood cells
• Hematocrit: Measures the proportion of red blood cells in the blood
• Serum ferritin: Reflects stored iron levels in the body

Iron stores can take months to become depleted. Ferritin typically declines before hemoglobin, meaning iron deficiency can exist without anemia.

When anemia develops, hemoglobin levels fall below normal, reducing oxygen transport throughout the body. Symptoms may include:

• Fatigue and exhaustion
• Irritability
• Shortness of breath
• Headaches
• Pale skin

Vitamin B12

Several blood tests can evaluate vitamin B12 status. Deficiency may result from insufficient intake or impaired absorption.

Possible complications include:

• Megaloblastic anemia, which causes typical anemia symptoms (this can sometimes be masked by high folate intake)
• Neurological damage, including mood changes, confusion, tingling, numbness, and balance problems
• Gastrointestinal issues, such as loss of appetite, indigestion, and diarrhea
• Elevated homocysteine levels, increasing risk of cardiovascular disease, bone problems, and stroke

Long-term B12 deficiency can lead to serious neurological complications. Fortunately, B12 supplements are widely available, safe, and not associated with toxicity at recommended doses.

Iodine

Urine testing can assess iodine intake in individuals following a vegan diet. Because about 90% of dietary iodine is excreted in urine, urinary iodine is a reliable indicator of status.

Iodine deficiency can lead to hypothyroidism, characterized by a slowed metabolism. It may also cause enlargement of the thyroid gland (goiter) as the body attempts to capture more iodine.

Other symptoms may include skin issues, weight gain, and elevated cholesterol.

Plant foods typically contain less iodine than animal foods such as dairy, eggs, and fish. However, in Canada, iodized salt provides a safe, effective, and affordable way to meet iodine needs.

If you are unsure about your intake, consulting a dietitian can help optimize your nutrition and prevent deficiencies.

Absorption vs Intake: The Question That Truly Matters

Beyond the amount consumed, nutrient absorption plays a crucial role. It is a common misconception that everything we eat is fully absorbed.

Type of Iron

• Heme iron (from animal foods) is better absorbed (15–35%)
• Non-heme iron (from plant foods such as legumes, leafy greens, and grains) is less efficiently absorbed (2–20%)

Factors That Limit Absorption

• Calcium reduces iron absorption when consumed together
• Tea and coffee decrease iron absorption
• Oxalates and phytates reduce calcium absorption
• Intrinsic factor — a protein produced by the stomach — is required for vitamin B12 absorption; deficiency impairs B12 uptake

Factors That Enhance Absorption

• Vitamin C increases non-heme iron absorption
• Vitamin D improves calcium absorption

Why Supplements Alone Often Fall Short

The nutritional supplement market continues to grow rapidly, reaching 2M$ in sales in 2023 in Canada alone! That said, supplements alone are not a complete solution for optimal health.

Whole foods contain a complex matrix of nutrients, including antioxidants and phytochemicals, that enhance the effectiveness of vitamins and minerals. Supplements do not provide these synergistic compounds.

The most effective approach is a balanced, varied vegan diet combined with targeted supplementation, particularly vitamin B12 and vitamin D (especially in northern countries).

Because individual needs vary, consulting a dietitian can help determine whether additional supplements are necessary.

How a Dietitian Develops a Corrective Plan

When you consult a vegan dietitian from our team, you receive personalized guidance designed to meet your specific nutritional needs.

The process is structured and evidence-based:

First, we conduct a comprehensive assessment of your blood work, dietary habits, lifestyle, and health history. This evaluation allows us to create an individualized nutrition plan tailored to your reality.

Dietitian support helps you maintain a simple, balanced diet without unnecessary complexity. We can also guide you in selecting appropriate supplements if needed.

If you have concerns about your nutrition, don’t wait, consult a member of our team of dietitians.