Vitamin C test: when it is done and what the result means

Vitamin C, or ascorbic acid, is a water-soluble vitamin that the body does not make on its own — it has to be obtained from food, especially fresh fruit and vegetables. It takes part in producing collagen (important for the skin, blood vessels, gums and bones), acts as an antioxidant, and helps the body absorb iron from plant foods better. Because vitamin C is not stored in the body in large amounts, its reserves can run down fairly quickly if the diet is poor for a long time. The blood test that measures the concentration of vitamin C (ascorbic acid) is used less often than, for example, vitamin D or B12 tests — most often it is done when a marked dietary shortage or scurvy is suspected, not as a routine preventive test. It is always worth assessing the result together with eating habits, lifestyle (smoking, alcohol use) and overall health, and the final assessment is made by a doctor.

• When scurvy is suspected — when there is persistent tiredness, bleeding or swollen gums, easy bruising
• When the diet has lacked fresh fruit and vegetables for a long time
• In people who smoke, or who have used alcohol heavily over a long period, whose nutritional state is in doubt
• In pregnant or breastfeeding women whose diet is limited
• When assessing overall nutritional status together with other trace element and vitamin tests

A widely recognised, publicly published international blood reference range for vitamin C (µmol/l) could not be confirmed from a reliable source at this time, so you will find the specific range your laboratory uses on your own result sheet — it can differ depending on the method.

A high vitamin C result

A raised vitamin C level in blood is rare and is most often linked to taking large amounts of supplements rather than to food. Vitamin C is water-soluble, so an excess usually leaves the body in the urine. The NHS states that very large amounts from supplements can cause short-term digestive upsets.

Causes listed for a high result:

• Taking large amounts of vitamin C supplements, for example to boost immunity
• Combining vitamin C supplements with iron supplements, when the aim is to improve iron absorption
• Rarer cases in which the body has difficulty clearing water-soluble vitamins

Possible symptoms:

• Stomach pain
• Diarrhoea
• Increased gas

What to discuss with a doctor:

• Discuss with your doctor or pharmacist the amounts of the supplements you take and whether they are warranted
• If you take supplements together with iron preparations, discuss this with your doctor
• If you plan to take large amounts of supplements for a long time, ask about monitoring kidney function

A lowered vitamin C level in blood shows that not enough ascorbic acid is being obtained from food. According to the NHS, a long-lasting shortage can cause scurvy — a condition with tiredness, bleeding gums and easy bruising. Most often this is linked to a long period of poor nutrition.

Causes listed for a low result:

• A diet without fresh fruit and vegetables over a long period
• Smoking
• Long-term dependence on alcohol or other substances that disrupts normal eating
• Poor nutrition during pregnancy or breastfeeding

Possible symptoms:

• Persistent tiredness and weakness
• Swollen, bleeding gums (teeth can sometimes fall out)
• Easy bruising

What to discuss with a doctor:

• Discuss your eating habits with your doctor or a dietitian
• Discuss whether a vitamin C supplement is needed, and in what form
• Assess how smoking and alcohol use affect your nutritional state
• Check other nutrition-related markers if a wider shortage is suspected

Related pages

Vitamin A test, active B12 test, hs-CRP test.