Understanding What Happens When Vitamin D2 Is Low: A Nutritional Perspective

October 15, 2025 •

4 min read

According to the National Institutes of Health, obtaining sufficient vitamin D from diet and sunlight can be difficult for many people. When vitamin D2 levels are low, the body's ability to absorb calcium is severely compromised, impacting bone health, muscle function, and overall well-being. This guide explores the specific consequences of a vitamin D2 deficiency and how to manage it through proper nutrition and supplementation.

Quick Summary

A deficiency in vitamin D2 impairs calcium absorption, leading to weakened bones and conditions like rickets or osteomalacia. Symptoms include muscle pain, fatigue, and mood changes. A blood test can confirm low levels, which are addressable through dietary adjustments and supplements, often using vitamin D3 for better absorption.

Key Points

Impaired Calcium Absorption: A deficiency in vitamin D2 significantly reduces the body's ability to absorb calcium, which is crucial for bone health.
Increased Risk of Bone Diseases: Low vitamin D2 levels can lead to rickets in children and osteomalacia or osteoporosis in adults, resulting in weak, soft, or brittle bones.
Muscular Problems: A deficiency can cause muscle weakness, aches, and cramps, increasing the risk of falls, especially in older individuals.
Systemic Symptoms: Beyond bone and muscle issues, low vitamin D2 is associated with fatigue, depressed mood, and impaired immune function.
Management via Supplementation: The condition is treatable with vitamin D supplements (D2 or D3), dietary changes, and, with caution, sun exposure.
Professional Diagnosis: Diagnosis requires a blood test to measure 25-hydroxyvitamin D levels, and treatment plans should be supervised by a healthcare provider.

The Critical Role of Vitamin D in Your Body

Vitamin D is a fat-soluble vitamin essential for numerous physiological functions, primarily the regulation of calcium and phosphate in the body. These minerals are fundamental for maintaining healthy bones, teeth, and muscles. The body can obtain vitamin D in two forms: vitamin D2 (ergocalciferol), sourced from plants and mushrooms, and vitamin D3 (cholecalciferol), produced in the skin upon sun exposure or found in some animal-based foods and supplements. Both forms must be converted by the liver and kidneys into the active form, 25-hydroxyvitamin D.

When levels of vitamin D, including D2, are insufficient, the body’s ability to absorb calcium from the intestines decreases significantly. To maintain blood calcium balance, the body compensates by producing more parathyroid hormone (PTH), which triggers the release of calcium stored in the bones. This process, if prolonged, leads to accelerated bone demineralization and a host of health complications.

Health Consequences of Low Vitamin D2

The effects of a vitamin D2 deficiency are systemic, impacting not only the skeletal system but also muscle function, immune health, and mood.

Skeletal and Muscular Effects

Rickets in Children: In growing children, severe vitamin D deficiency causes a bone-softening condition called rickets. This can lead to deformities such as bowed legs, stunted growth, and bone pain. The bones become soft and pliable, unable to support the body's weight correctly.
Osteomalacia in Adults: For adults, the equivalent condition is osteomalacia, characterized by weak and soft bones due to inadequate mineralization. Symptoms often include widespread bone pain and tenderness, which may be misdiagnosed as other conditions like fibromyalgia.
Osteoporosis: Chronic deficiency contributes to osteoporosis, a condition where bones become thin, brittle, and susceptible to fractures. The increased bone turnover caused by elevated PTH levels speeds up this process.
Muscle Weakness and Pain: Vitamin D receptors are present in muscle tissue, and a deficiency can lead to proximal muscle weakness, aches, and cramps. This can increase the risk of falls, particularly in older adults.

Wider Systemic Impacts

Fatigue and Mood Changes: Persistent fatigue and low mood are common, non-specific symptoms of a deficiency. There is a link between low vitamin D and mood disorders like depression, though the direct causal relationship is still under investigation.
Impaired Immune Function: Vitamin D plays a key role in modulating the immune system. Insufficient levels are associated with increased susceptibility to infections and autoimmune diseases.
Other Chronic Conditions: Observational studies have linked poor vitamin D status to a greater risk of various chronic diseases, including cardiovascular disease, certain cancers, and diabetes.

Comparing Vitamin D2 and Vitamin D3

While both forms of vitamin D function similarly in the body, there are some differences to note, particularly regarding their sources and effectiveness in raising serum levels.


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Primary Source	Plant-based sources, such as mushrooms, and fortified foods.	Animal-based sources (fatty fish, eggs) and synthesized in skin from sunlight exposure.
Effectiveness	Considered slightly less effective than D3 in raising serum vitamin D levels long-term, though both are viable options.	May raise and maintain serum vitamin D levels more effectively than D2.
Availability	Prescription-strength doses are available by prescription.	Available over-the-counter and in fortified foods.

How to Address a Low Vitamin D2 Level

If a blood test reveals low vitamin D levels, a healthcare provider will recommend a course of action to restore them. A severe deficiency may require high-dose supplementation for a period of weeks to correct the deficit.

Steps for Treatment and Prevention

Supplements: Vitamin D supplements, available as D2 (ergocalciferol) and D3 (cholecalciferol), are the most direct way to raise levels. Your doctor will determine the appropriate dosage.
Dietary Adjustments: Incorporate more vitamin D-rich foods into your diet. Sources of D2 include UV-exposed mushrooms, while sources of D3 include fortified milk, cereals, and fatty fish like salmon.
Safe Sun Exposure: While not a sole solution due to skin cancer risks, brief, regular sun exposure can help your body produce vitamin D.

Conclusion

Low vitamin D2 levels, a component of overall vitamin D deficiency, can lead to serious health problems affecting the bones, muscles, and overall systemic health. From triggering bone-weakening conditions like rickets and osteomalacia to contributing to fatigue and mood changes, the consequences of a deficiency are significant. The good news is that this condition is both preventable and treatable through proper supplementation and dietary choices. If you suspect you have low vitamin D, consulting a healthcare professional for a blood test is the first step toward restoring your levels and protecting your long-term health.

Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a healthcare provider for diagnosis and treatment.

Frequently Asked Questions

Vitamin D2 (ergocalciferol) comes from plant sources like mushrooms, while vitamin D3 (cholecalciferol) is produced in the skin from sunlight exposure and is found in animal products. Both are used in supplements, but some research suggests D3 is more effective at raising and maintaining vitamin D levels.

Initial symptoms can be subtle and non-specific, including general fatigue, bone pain, muscle aches, and mood changes like depression. Many people with mild deficiency may not notice any symptoms at all.

Yes, low vitamin D levels have been linked to an increased risk of mood disorders such as depression. While the exact nature of this connection is still being researched, some studies suggest that vitamin D supplementation can improve mood in deficient individuals.

A low level of vitamin D is typically diagnosed with a blood test that measures the concentration of 25-hydroxyvitamin D. Your doctor can order this test if they suspect a deficiency based on your symptoms or risk factors.

Few foods naturally contain high amounts of D2, but UV-exposed mushrooms (like portobello, maitake, and shiitake) are a significant source. Some fortified foods, such as milk, cereals, and orange juice, may also contain added D2.

The most common ways to increase vitamin D are through supplements, eating vitamin D-rich or fortified foods, and getting safe, moderate sun exposure. Your doctor can provide personalized recommendations based on your blood test results.

While both can be effective, some evidence suggests that D3 supplements may be more potent at raising and maintaining vitamin D levels in the blood. The choice between D2 and D3 may also depend on dietary preferences, as D2 is plant-based while D3 often comes from animal sources.