More than just vision
Most people associate vitamin A with eyesight, and for good reason — retinol is essential for the production of rhodopsin, the photopigment that enables low-light vision. But vitamin A plays an equally critical role in immune function, skin integrity, reproductive health, and gene expression. It supports the differentiation of epithelial cells throughout the body and is necessary for a functioning adaptive immune response.
This means that suboptimal vitamin A levels can manifest in ways that are easily attributed to other causes: frequent infections, slow wound healing, dry skin, and impaired fertility. Without direct measurement, clinicians may overlook retinol status entirely.
The global burden of deficiency
The World Health Organization estimates that vitamin A deficiency affects approximately 190 million preschool-age children and 19 million pregnant women worldwide, predominantly in low- and middle-income countries. In these populations, deficiency is a leading cause of childhood blindness and contributes significantly to morbidity and mortality from infectious diseases such as measles and diarrhoea.
In high-income countries, clinical vitamin A deficiency is rare, but subclinical insufficiency is more common than generally recognised — particularly among individuals with fat malabsorption conditions (such as coeliac disease, Crohn's disease, or cystic fibrosis), chronic liver disease, or restrictive diets that exclude animal-source foods.
What does the test measure?
Vitamin A status is assessed by measuring serum retinol — the primary circulating form of the vitamin. Retinol levels below 0.70 µmol/L (20 µg/dL) indicate deficiency, while levels between 0.70 and 1.05 µmol/L represent marginal status. At Masdiag, we quantify retinol using LC-MS/MS from a dried blood spot, providing precise, reference-grade results without the need for venous collection.
One important nuance: serum retinol is tightly regulated by the liver, meaning that levels remain relatively stable until liver stores are significantly depleted. By the time circulating retinol drops, the body's reserves may already be critically low. This is why periodic testing is valuable for at-risk populations — it catches depletion before clinical symptoms appear.
The toxicity question
Unlike water-soluble vitamins, vitamin A is fat-soluble and can accumulate to toxic levels — a condition known as hypervitaminosis A. Chronic excessive intake (typically from high-dose supplements rather than food) can cause liver damage, bone loss, headaches, and in severe cases, intracranial hypertension. Testing is therefore important not only for detecting deficiency but also for monitoring individuals who supplement with preformed vitamin A (retinyl palmitate or retinyl acetate) to ensure levels remain within the safe range.
Who should consider testing?
Testing is particularly relevant for individuals with gastrointestinal conditions that impair fat absorption, those with chronic liver disease, people following strict vegan or plant-based diets (where preformed retinol is absent), pregnant women in regions with high deficiency prevalence, and anyone supplementing with high-dose vitamin A who needs to confirm they are within safe limits. For researchers studying nutritional status in population cohorts, dried blood spot testing offers a practical, scalable alternative to traditional serum collection.
Frequently asked questions
What is a normal vitamin A level?
Serum retinol levels below 0.70 µmol/L (20 µg/dL) indicate deficiency, while 0.70–1.05 µmol/L represents marginal or insufficient status. Levels above 1.05 µmol/L are considered adequate. For optimal health, particularly in populations at risk of deficiency or malabsorption, levels above 1.2 µmol/L are often targeted. Individual needs vary based on health status, liver function, and degree of prior depletion.
Can you have too much vitamin A?
Yes, vitamin A toxicity (hypervitaminosis A) can result from chronic excessive intake, particularly from high-dose supplements or medications containing retinoid compounds. Symptoms include liver damage, bone loss, joint pain, headaches, and in severe cases, intracranial hypertension. Toxicity is rare from food sources and sun exposure but possible from supplemental preformed vitamin A taken in doses exceeding 10,000 IU daily over extended periods.
Who is at risk of vitamin A deficiency?
High-risk populations include people with fat malabsorption conditions (coeliac disease, Crohn's disease, cystic fibrosis), those with chronic liver disease, individuals on very restrictive diets excluding animal-source foods, premature infants, and pregnant women in regions with high deficiency prevalence. Testing is valuable for screening these populations before deficiency causes irreversible damage like blindness.
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