Vitamin A: what it is, what it tells you and when it’s tested

Vitamin A keeps your eyes working, especially in the dark, and supports your skin, your defences against infection and growth. Your body stores it in the liver. The blood test measures retinol, its main form.

When it’s tested

Doctors order it when they suspect a shortage: with conditions that absorb fat poorly, such as coeliac disease or pancreas disease, after weight-loss surgery, with liver disease or a very poor diet. They also order it if you see poorly in the dark for no clear reason.

They also order it when they suspect too much, for example in people who take high-dose supplements or medicines similar to vitamin A.

It is not a routine test for people who feel well. In Italy a shortage is rare, and the blood level only changes when the stores are nearly empty or really too high. That is why Rosa does not test it. Instead it looks at vitamin D, another vitamin that dissolves in fat, and at the liver, which stores it.

What it tells you, and what it does not

Your liver keeps retinol in your blood almost constant. So the value only falls when the stores are nearly empty, and only rises when they are really too high.

A normal value does not tell you whether your stores are right, low or a little too high. And an infection or inflammation can lower it even when your stores are fine.

That is why it is read together with other tests:

• Vitamin D: It also dissolves in fat and is short with the same conditions
• Vitamin E: Another vitamin absorbed with fat
• ALT and AST: Your liver stores vitamin A, and too much damages it
• Anti-transglutaminase antibodies: They look for coeliac disease, a cause of poor absorption

Normal vitamin A levels

The lab decides what is normal. Some lab reports give 0.30 to 0.70 mg/L in adults, the same for men and women. In children the limit is lower.

Some labs write µg/mL, which gives the same number. Others use µg/dL or µmol/L, with different numbers. The range printed next to your result is what counts.

The blood test is done fasting, and the sample must be kept out of the light.

What your result means

Find the row for your result, in mg/L or µg/mL. Below 0.20 is low by international cut-offs too; below 0.10 the stores are nearly empty.

• Below 0.10: Very low. The stores in your liver are nearly used up. This is rare in Italy: usually a bowel that absorbs fat poorly, a liver condition or a very poor diet is behind it. See your doctor within a few days, especially if you see poorly in the dark.
• 0.10 to 0.20: Low. Your body may be short of it. An ongoing infection or inflammation also lowers it. Talk to your doctor: they look for the cause and, if needed, repeat the test.
• 0.20 to 0.30: Slightly below normal. Often not a real shortage. A cold, an infection or inflammation can lower it for a while. Show it to your doctor. It is usually repeated once you are well.
• 0.30 to 0.70: Normal. Your body has enough. A normal value does not rule out too much, though: your liver keeps the blood level steady even when the stores are too high. Nothing to do.
• Above 0.70: High. It usually comes from supplements that contain vitamin A. When it is high, the stores in your liver may really be too high. Talk to your doctor and bring the list of your supplements. If you are pregnant or trying for a baby, talk to your gynaecologist straight away too.

If your vitamin A is low or high

• Low vitamin A: Often an infection or inflammation. A real shortage usually comes from a bowel or liver that is not working well.
• High vitamin A: It usually comes from supplements. Too much is toxic to your liver and bones, and dangerous in pregnancy.

What lowers it and what raises it

The most common causes, those of a low value first:

• Infections and inflammation: They lower the value for a while, even when your stores are fine.
• A bowel that absorbs fat poorly: Coeliac disease, pancreas or bile duct disease, weight-loss surgery.
• Liver disease and alcohol: Your liver stores vitamin A. When it is diseased, it stores and releases less.
• A very poor diet: Few animal foods and few coloured vegetables, for a long time.
• Supplements: The most common cause of a high value, especially if you take more than one.

Symptoms of too little and too much

A shortage can cause:

• Vision that gets worse in the dark, dry eyes
• Dry, rough skin
• More frequent infections

Too much, on the other hand, can cause headaches, nausea, dry peeling skin, bone pain and, over time, liver damage. Either way, talk to your doctor.

Too much vitamin A: why it is a risk

Ready-made vitamin A, the kind in animal liver and in supplements, builds up. Too much for months damages your liver and weakens your bones, with a higher risk of fractures.

In pregnancy, too much ready-made vitamin A, especially from supplements in the first weeks, is linked to birth defects. If you are pregnant or trying for a baby, do not take supplements with vitamin A without talking to your doctor or gynaecologist.

Beta-carotene from vegetables is different: your body turns it into vitamin A only when it needs to.

Where it is found: what to eat

Vitamin A comes in two forms:

• Ready-made, in animal foods: liver, which is very rich in it, eggs, butter, whole milk and cheese
• As beta-carotene, in plants: carrots, pumpkin, sweet potatoes, melon, apricots, spinach and other leafy greens

A varied diet is usually enough. Do not take vitamin A supplements without a reason: ask your doctor.

What can skew the result

A few things change the value without changing your stores.

• A current infection: Even a cold or a fever lowers it for a while.
• A meal: Eating shortly before the blood test can change the value. That is why it is done fasting.
• A tube left in the light: Vitamin A breaks down in light. The lab protects the sample.
• Kidneys and liver: Kidney or liver disease changes the value. Your doctor takes it into account.

When to worry

Talk to your doctor if:

• Your vitamin A is below or above the range on your report.
• Your vision in the dark keeps getting worse, or your eyes are very dry.
• You take one or more supplements with vitamin A and have headaches, peeling skin or bone pain.
• You are pregnant or trying for a baby and take supplements: talk to your gynaecologist too.
• A child has swallowed a lot of supplements or vitamin tablets: call 112 or go to the emergency department.

Frequently asked questions

What does vitamin A do? It keeps your eyes working, especially in the dark, and supports your skin and mucous membranes, your defences against infection and growth.

What are normal vitamin A levels? Some lab reports give 0.30 to 0.70 mg/L in adults. The range printed on your own report is what counts, and it may use another unit.

Which foods contain vitamin A? Ready-made in liver, eggs, butter, milk and cheese. As beta-carotene in carrots, pumpkin, sweet potatoes, melon, apricots and leafy greens.

Is vitamin A dangerous in pregnancy? Vitamin A is needed in pregnancy too, but too much ready-made vitamin A, especially from supplements, can cause birth defects. Before taking supplements, talk to your doctor or gynaecologist.

What does high vitamin A mean? It usually comes from supplements. Because your liver keeps the level steady, a high value can mean your stores are really too high. Talk to your doctor.

Does Rosa test vitamin A? No. Rosa measures vitamin D, ALT and AST and gamma GT, which say a lot about fat-soluble vitamins and your liver. If your doctor wants vitamin A, they order it separately.

Sources

• ASST Grande Ospedale Metropolitano Niguarda, laboratory test catalogue: vitamin A, reference values. Catalogo esami Niguarda
• Centro Diagnostico Italiano, test sheet: vitamin A, reference values. Scheda esame CDI
• World Health Organization, serum retinol concentrations for determining the prevalence of vitamin A deficiency in populations. VMNIS, 2011. WHO/NMH/NHD/MNM/11.3
• Penniston and Tanumihardjo, the acute and chronic toxic effects of vitamin A. American Journal of Clinical Nutrition, 2006. PMID 16469975
• Rothman and colleagues, teratogenicity of high vitamin A intake. New England Journal of Medicine, 1995. PMID 7477116