Vitamin B6: immunity star, or not?

vitamin b6Nutrition research can often be tantalising.

In the early stages, when researchers discover new functions for well-known nutrients, but there is not yet an overwhelming body of evidence available, we know that a nutrient may have new and important roles to play.

However, we can't as yet recommend exactly how much of the nutrient would be required to achieve its protective or curative function. At present, this applies to vitamin B6.

Background info on vitamin B6
Vitamin B6, also called pyridoxine, has been known since 1934 when a researcher discovered that the vitamin cured scaly dermatitis in rats fed a diet lacking B6.

a) Many functions
We also know that vitamin B6 interacts with more than 100 enzymes acting as a catalyst for many different biochemical reactions. Vitamin B6 is a particularly important catalyst in amino acid metabolism and assists the function of certain hormones.

b) Deficiency
Vitamin B6 deficiencies can be caused by malabsorption, chronic alcoholism, and coeliac disease, and it occurs in renal patients undergoing dialysis. However, it is estimated that up to 20% of the general population suffer from chronic vitamin B6 deficiencies.

The symptoms of such chronic vitamin B6 deficiencies include:

  • Inflammation of the tongue, with sores on the lips and corners of the mouth.
  • So-called microcytic hypochromatic anaemia (anaemia characterised by small, pale red blood cells).

Vitamin B6 deficiencies have also been linked to the development of heart disease and cancer of the breast, uterus and prostate.

Older people tend to have lower vitamin B6 blood levels, which may indicate poor dietary supply or uptake or an increased requirement.

c) Drug interactions
Certain medications can deplete the body of vitamin B6, particularly the anti-TB drug isoniazid, penicillamine which is used to treat rheumatoid arthritis, and anti-parkinsonism drugs such as benserazide and carbidopa (Garrow et al, 2000).

Some studies have also indicated that old-fashioned contraceptive pills, which contained high levels of oestrogen, were capable of causing vitamin B6 deficiencies.

d) RDA
According to Garrow and coauthors (2000), the Recommended Daily Allowance (RDA) for vitamin B6 or pyridoxine in adults is 3,5mg per day, while the South African RDA is 2mg per day for adults.

e) Food sources
Vitamin B6 occurs in most foods, but the highest levels are found in:

  • Beef liver, chicken, turkey, pork and fish.
  • Oatmeal, brown rice, wheat germ and other whole-grains.
  • Fruits such as banana, avocado, prunes and vegetables such as potatoes.
  • Sunflower seeds, legumes, and nuts.

In general, vitamin B6 is more easily absorbed from foods derived from animals, such as liver, beef, poultry, and fish.

f) Use of vitamin B6 supplements
Vitamin B6 supplements have been used to treat a variety of conditions, including premenstrual syndrome (PMS), postnatal depression, depression, vomiting during pregnancy and carpal tunnel syndrome (100mg/day).

Because higher doses of vitamin B6 counteract nausea, this vitamin has been widely used at doses varying between 50-200mg per day to reduce nausea in cancer patients undergoing radiotherapy.

g) Toxicity
A word of warning: at very high doses, vitamin B6 can be toxic and can damage the nerves.

It is, therefore, not a good idea to take vitamin B6 supplements which contain more than the RDA of 2mg per day unless prescribed by a medical doctor for conditions such as PMS or nausea associated with radiotherapy.

New research findings
Recent research, such as a study conducted in Taiwan with critically ill patients in an ICU, demonstrated that high doses (50-100mg/day) of vitamin B6 boosted the immunity of these patients.

In some cases, the so-called 'markers of immunity' increased by nearly 100% in the patients who received vitamin B6 supplementation (Arbor, 2007).

Another Taiwanese study (Arbor, 2007) showed that a variety of immune markers (such as neutrophils and T and B lymphocytes – blood cells that help the body to fight disease) increased as the vitamin B6 levels of the patients increased.

However, an American study investigating the link between vitamin B6 status and rheumatoid arthritis, found that in patients with rheumatoid arthritis who were given 50mg of vitamin B6 for 30 days, low blood levels of vitamin B6 improved, but that this supplementation did not have any effect on the patients' inflammatory disease (Arbor, 2007).

Vitamin B6 and immunity
It has been known for quite a while that changes in vitamin B6 status, even in healthy subjects, can affect how lymphocytes multiply and react to immune challenges (Arbor, 2007).

The American study mentioned above showed that vitamin B6 levels in patients with rheumatoid arthritis are depressed and that daily supplementation with 50mg of vitamin B6 can correct these deficiencies.

The study did not, however, prove that vitamin B6 can assist in alleviating the inflammatory symptoms of this disease. So, until more studies have investigated the relationship between rheumatoid arthritis and vitamin B6, we can't yet recommend that all patients with rheumatoid arthritis should take vitamin B6 supplements.

If you do suffer from rheumatoid arthritis, it may be a good idea to ask your doctor to test your vitamin B6 levels and if these should be depressed, to take a supplement under the doctor's supervision.

A number of studies have also reported that depressed vitamin B6 levels in patients with HIV/Aids results in more rapid progression of this disease, vertical transmission and less positive immune responses (Arbor, 2007).

Once again, nutritionists are not yet in a position to recommend that all patients suffering from HIV/Aids should take vitamin B6 supplements, but we can recommend that such patients should try to ensure that their diet contains foods rich in vitamin B6 such as chicken, turkey, pork, fish, avocados, bananas and nuts.

For the general public, the same applies: make sure that your diet contains foods that are rich in vitamin B6 as listed above. If you have to take any of the drugs that deplete vitamin B6 (anti-TB, anti-parkinsonism and rheumatoid arthritis drugs and possibly also contraceptive pills), then ask your doctor to monitor your vitamin B6 blood levels and to prescribe a supplement if they are too low.

Text copyright: Dr I.V. van Heerden (DietDoc), 5 February 2007

(Arbor Clinical Nutrition Updates, 2007. Vitamin B6 and immunity. Edition 269:1-3; Garrow et al (2000). Human Nutrition & Dietetics, 10th Edition, Churchill Livingstone, Edinburgh )