Positive Health Online

Vitamin A is not a vitamin that currently gets much publicity. This is because deficiency in developed countries is considered rare. The same thinking used to apply to Vitamin D, but now it is known that most of us in the UK are not getting enough vitamin D. The same change of attitude is needed for vitamin A.

Beta carotene, the vegetable form of vitamin A, from which the body makes vitamin A ‘proper’ or retinol, is found abundantly in plant foods which are widely available in the average diet. However as we will see, there are several factors affecting the conversion, metabolism and absorption of vitamin A.

Vitamin A deficiency has a profound negative impact on various aspects of health and wellbeing. Lack of vitamin A affects vision, skin, bones, immune system and lungs. Here are some common signs and symptoms to look out for, relating to vitamin A deficiency (they can also relate to other conditions which is why it’s advisable to consult a practitioner before self diagnosing):

• Dry flaky skin
• Cracked dry skin on heels
• Acne
• Brown pigmentation spots on the skin
• Mouth ulcers
• Poor vision especially at night 
• Frequent colds, viruses or infections
• Dandruff 
• Thrush
• Cystitis
• Diarrhoea
• Anaemia that persists despite taking iron supplements
• Psoriasis
• Atopic dermatitis
• Thyroid disorders
• Ear infections
• Dry eyes
• Vaginitis
• Arthritis
• Hyperkeratosis (thickening of the skin e.g. on elbows, upper arms and heels)
• Diabetes 
• Cervical dysplasia (abnormal)
• Inflammatory bowel disease (e.g. Crohns, colitis) & diseases affecting the intestines such as Coeliac disease, gluten sensitivity, giardia (parasite) infection.

Why is deficiency of vitamin A more common than previously thought?

• Poor Conversion The important fact to remember is that ‘vitamin A proper’ which is pre-formed vitamin A and known as retinol, is only found in animal derived food sources (cheese, egg yolk, oily fish and liver are the richest sources - yoghurt also contains some). Its cousin, beta carotene is found in plant foods, particularly orange and yellow fruits and vegetables and green vegetables.

In theory, if we eat fruit and vegetables which contain beta carotene we should be getting a plentiful supply of vitamin A. Beta carotene is converted into vitamin A by the body when needed. However, the truth is that whilst plenty of people do manage this conversion efficiently, there are many who don’t, leading to inadequate vitamin A levels. 

The scientific analysis of beta carotene conversion has advanced over the last few years. It was originally thought that the rate of conversion was 6:1 e.g. 6000 IU of beta carotene converts to 1000 IU of vitamin A. It has now been discovered that the conversion rate rather than being fixed, varies widely from one person to another. It has been found to be as low as 29:1 i.e. 12,000 IU of beta carotene converts into just 413 IU vitamin A.

Two studies found that 45% of two small groups separated into men and women, living in a controlled environment and eating healthily, did not show a measurable rise in their blood beta carotene levels after eating foods containing vitamin A. The authors concluded, “Vitamin A activity of beta-carotene, even when measured under controlled conditions, can be surprisingly low and variable.”

Another study lasting 4 years found that after giving high levels of beta carotene (41,000 IU per day) to a varied group of people, there was no significant increase in blood levels of vitamin A (retinol).

People with underactive thyroid glands tend to accumulate beta carotene, an indication of poor conversion to vitamin A. This leads to patches of yellow skin, particularly on the soles of the feet and palms of the hands and in the creases of the nose. Anorexics and diabetics also have impaired vitamin A conversion. High alcohol consumption also blocks conversion. Vegetarians with an underactive thyroid are at particular risk of low vitamin A.

• Low Fat Intake
  Low fat diets are still fashionable for weight loss and this will lead to low vitamin A status, as this vitamin can only be absorbed in the presence of fat since it is fat soluble. Adding flax or hemp oil to vegetables that are not hot will help absorption.
• Lack of Zinc
  Low zinc levels will predispose to low vitamin A since these two nutrients work together. Zinc is found in meat, fish and pumpkin seeds. Non meat and fish eaters have a challenge to obtain adequate zinc.

The Vital Functions of Vitamin A

Let’s remind ourselves of what vitamin A does in the body.

Vitamin A and Immune Health

Vitamin A  has a special relationship to healthy immunity. First, it strengthens the delicate outer membranes of the nose, throat, digestive tract and lungs. These membranes are the first line of defence against attack from the outside. It’s also needed for the healthy membranes of the eyes, ears and reproductive organs. Vitamin A should therefore be thought of in the case of sinus, ear, eye, throat, lung, vaginal, ovarian, uterine or prostate infections.

Second, it enhances the action of the immune cells, shortening the duration of illness. Vitamin A deficiency increases the risk of infection.

So if you are someone who is always catching the latest bug you may need more vitamin A.

Vitamin A and Leaky Gut

The lining of the intestine (epithelium) in its healthy state consists of densely packed cells like bricks in a wall. ‘Sheets’ of bricks are joined together at tight junctions. If the epithelium becomes damaged (e.g. by toxins, drugs, food intolerances or parasites), it becomes too permeable, allowing substances to pass through the junctions in the gut wall into the blood. This then triggers an immune response. Leaky gut is a new research area. There are significant recent studies which suggest that a leaky gut is a major factor in auto immune diseases such as rheumatoid arthritis. Vitamin A is an important factor in maintaining a healthy gut lining.

Vitamin A and Iron Deficiency

Vitamin A is vitally important in the metabolism of iron. In one of the earliest human studies, adults on a vitamin A deficient diet developed anaemia despite adequate iron intake.  The anaemia responded to vitamin A but not to iron.

So anyone with low iron should consider vitamin A supplements (especially if iron supplementation alone has not successfully raised iron levels sufficiently).

What to look for in Supplements

As an unfortunate result of scare stories and misinterpretation of the research concerning vitamin A, most UK supplement companies now use beta carotene and not preformed vitamin A .This means the majority of multivitamins available do not contain vitamin A. 

How Much Do I Need?

The UK recommended daily intake for adults is approximately 600mcg (2,300IU ).

However it is going to depend very much on the individual, taking into account the factors above relating to vulnerability to deficiency. In many cases a higher intake may be required.

Food Sources

Carotenoids  are found abundantly in green leafy vegetables, orange and yellow fruit and vegetables. Carotenoids are better absorbed when the food is cooked and served with fat. The healthiest way to do this is to add a spoonful of extra virgin olive oil, flax oil or hemp oil onto vegetables that are lukewarm rather than hot so as not to change the beneficial fats in the oil into toxic compounds. The richest sources of pre formed Vitamin A are oily fish, liver, eggs and cheese. Yoghurt and meat also contain vitamin A.

Testing Vitamin A Levels

The normal range for retinol in the blood is 28 to 86 μg/dL. However, testing for vitamin A is not particularly useful because deficiency will only show up when it is advanced and severe. This is because the liver stores large quantities of vitamin A.

References

Ribaya-Mercado JD., et al. Carotene-rich plant foods ingested with minimal dietary fat enhance the total-body vitamin A pool size in Filipino schoolchildren as assessed by stable-isotope-dilution methodology. Am J Clin Nutr: 85:1041–9. 2007.

Tang G, Qin J, Dolnikowski GG, Russell RM. Short-term (intestinal) and long-term (whole-body) conversion of β-carotene to vitamin A in adults as accessed by a stable isotope reference method. Am J Clin Nutr: 78:259–66. 2003.

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Hickenbottom SJ, et al. Variability in conversion of ß-carotene to Vitamin A in men as measured by using a double-tracer study design. American Journal of Clinical Nutrition: 75(5): 900-907. May 2002.

Nirenberg DW et al. Effects of  4 years of oral supplementation with beta-carotene on serum concentrations of retinol, tocopherol, and five carotenoids. American Journal of Clinical Nutrition: 66(2): 315-9. Aug 1997.

Brubacher GB, et al. The vitamin A activity of beta-carotene. International Journal of Vitamin and Nutrition Research: 55(1):5-15. 1985.

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Mejia LA, et al. Vitamin A deficiency and anaemia in Central American children. American Journal of Clinical Nutrition: 30:1175-84. 1977.

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Arora P, et al. Vitamin A status in children with asthma. Pediatrics and Allergy Immunology: 13(3): 223-6. Jun 2002.

Roodenburg AJC et al. Comparison between time dependent changes in iron metabolism of rats as induced by marginal deficiency of vitamin A or iron. Br J Nutr: 71:687. 1996.