מהם היתרונות של ויטמין A?

What is vitamin A?

Vitamin A is a fat-soluble vitamin that cannot be synthesised in the body, meaning we have to consume it as part of our diets.

Preformed vitamin A, also known as retinol and retinal esters, can be used in the body without undergoing any changes first. These are usually found in meat, dairy products, and fish.

"Provitamin versions, scientifically known as beta carotene, need to be converted to its active form retinol before it can be used by the body," explains Dr Deborah Lee from Dr Fox Online Pharmacy. In a nutshell, this means your body has to convert it before it can use it.

This form of vitamin A is found in most brightly coloured fruit and vegetables such as leafy greens, carrots, peppers, and tomatoes.

"Once ingested in the diet, vitamin A is absorbed into the bloodstream in the small intestine. Because it is a fat-soluble vitamin, it is best absorbed after eating a meal containing fat, but this doesn't need to be a huge amount," Dr Lee says.

"Adding nuts, avocado, or a small dash of olive oil to a meal, is all that's required."

Vitamin A benefits

Dr Lee says it has several essential functions in the body: "It plays a role in the functioning of the immune system, it stimulates and maintains cell growth, and in reproduction it is vital for successful cell division in the ovaries and testes.

"Vitamin A has been found to be intricately involved in the growth, maturation, and differentiation of many different cell lines in the body, including those in the heart, lungs, and eyes.

"In the eye it is the precursor to the production of rhodopsin, the photopigment found in the rods of the retina which enable night vision. As a result, vitamin A deficiency can cause night blindness. Vitamin A also maintains the health of the cornea and the conjunctiva - the cells and membranes that cover the front of the eye."

There you have it - eating your carrots really does help you see in the dark.

What happens if you don't eat enough vitamin A?

Dr Lee says vitamin A deficiency is rare in the UK, but some groups are more at risk.

"These include women who are pregnant or breastfeeding, and young children and toddlers. Also, those with malabsorption from a variety of causes such as cystic fibrosis, coeliac disease, מחלת קרוהן או chronic pancreatitis, or after intestinal surgery - including bariatric surgery," she explains.

One study found around 29% of those with Crohn's disease had low vitamin A levels compared to 15% in the control group¹.

A 2019 review found patients who had undergone bariatric surgery were often deficient in a range of vitamins. Some 10-11% of those who had had a gastric bypass were lacking in vitamin A².

To supplement or not to supplement?

So now we know the vitamin A benefits - and what happens when you don't eat enough vitamin A - how can you ensure you are eating enough?

The simple answer is - if you're eating a healthy, balanced diet with plenty of brightly coloured fruit and vegetables, dairy products, or meat then you're getting enough vitamin A.

How much vitamin A per day?

Vegans and vegetarians can rest assured there is enough vitamin A in fruits and vegetables to keep them healthy.

It is recommended that adult men eat around 700 micrograms of vitamin A per day, and women eat 600 micrograms. You really don't need to eat that much to get the right amount in your diet³.

Foods high in vitamin A

• Brightly coloured fruit and vegetables - such as leafy greens, spinach, kale, broccoli, Brussels sprouts, lettuce, peppers, butternut squash, carrots, mangoes, papayas, and grapefruit.

• Dairy products - these are also often fortified with vitamin A.

• Meat - vitamin A is found in beef, calf, and lamb's liver.

• Oily fish - such as mackerel and salmon - but also fish oil supplements.

• Eggs.

Too much vitamin A

"If you eat a healthy, balanced diet, and are fit and well, there is no need to take vitamin A supplements, which could even be dangerous," Dr Lee says.

"You only need to take vitamin A supplements if you have a chronic medical condition as outlined above and have been told to do this under medical advice.

"Vitamin A supplements can cause problems as they can interact with some other types of medications," Dr Lee adds.

"For example, taking these alongside drugs such as acitretin, which is used in the treatment of psoriasis, or bexarotene, used to treat T-cell lymphoma, could lead to vitamin A toxicity, as these medicines are derived from vitamin A."

Dr Lee suggests speaking to your local pharmacist or GP before adding supplements to your diet, especially if you are on other medication.

קריאה נוספת

1. Mota et al; High prevalence of vitamin A deficiency in Crohn's disease patients according to serum retinol levels and the relative dose-response test.

2. Sema Çalapkorur and Hürmet Küçükkatirci; Vitamin deficiencies and prevention methods after bariatric surgery.

3. GOV.UK - Vitamin A.