Vitamins and minerals



 

      
 Vitamin
      and Mineral Supplementation
      - a
      guide to some of the more common contraindications



      The acute
      toxic effects of taking large amounts of vitamins and minerals
      over a short period of time are fortunately rare. However, the
      potential is there for it to happen if taking high dose or 'mega'
      single supplements (rather than the multivitamin/mineral variety).

      What are
      more worrying, are the unknown effects of taking supplements
      chronically i.e. over a long period of time. Also, there is the
      issue of nutrient-nutrient interaction, where the body absorbs
      more of one nutrient e.g. vitamin C enhances the absorption

      of iron
      in vegetarian diets; or may reduce the absorption e.g. high levels
      of zinc can interfere with copper resulting in a copper anaemia.

      What effects
      will this on health or performance? Remember too that food is
      also more than vitamins and minerals. Scientists are now beginning
      to find many other factors in food that are essential to health
      which are not yet fully understood. These new factors are not
      yet available in tablet form. Food is balanced chemistry; tablets,
      pills and powders are not.


Vitamin A 
Vitamin
      A - retinol

      Supplements containing
      more than 600µg (2000 i.u.) should be avoided in pregnancy
      and by women planning pregnancy unless advised by their doctor.
      Vitamin A may be contraindicated in people with kidney stones
      or a history of kidney stones. Vitamin A  beta carotene

      Smokers should be advised
      against beta-carotene supplementation. Excess carotenes may cause
      the skin to become yellow (including palms of feet and soles
      of hands).

Vitamin B

      Prolonged use of single B vitamin
      supplementation in high dosage may induce a deficiency insome
      other B vitamins. High intakes of B complex can cause stomach
      cramps, nausea and diarrhoea.

      Vitamin B2 (riboflavin) in larger amounts commonly
      causes a bright yellowing of the urine. This may effect laboratory
      blood tests. It will also be invalid as a method of testing hydration
      status.

      Vitamin B3 (niacin) intake above 100mg daily
      may aggravate stomach ulcers and cause a temporary flushing sensation.

      

      Vitamin B6 in amounts over 100mg a day over a period of
      time may cause a lack of sensation in the hands and feet, together
      with headaches.

      

      High intakes of folic acid
      supplements may mask vitamin B12 deficiency (a type of
      anaemia).

Vitamin C
Surplus vitamin C is
      excreted in the urine, but megadoses can cause stomach cramps,
      diarrhoea, headaches and sleep disturbances. Supplementing with
      more than 1000mg vitamin C is not advisable in women taking the
      oral contraceptive pill (may increase oestrogen). Continued high
      levels of vitamin C, if suddenly stopped may produce a 'rebound
      scurvy', suggesting a vitamin C deficiency. This is due the body
      getting used to high levels and failing to adapt when levels
      become lower.

Vitamin E
Daily intakes above
      100 i.u. in individuals with high blood pressure should be used
      under caution. Individuals with a recent history of heart disease
      should have high intakes supervised by their doctor.


Other
      minerals
 

      Calcium

      Will interact with iron in
      the short term. Large doses for treatment of bone problems need
      medical supervision as other nutrients may be needed in addition
      to calcium.


      Chromium

      Use with caution


      Copper

      Potentially toxic in large
      doses, causing liver and kidney damage


      Iron

      Single-dose iron supplementation
      should be medically prescribed. Iron can accumulate in the body
      and long-term use needs to be monitored carefully. Inorganic
      iron supplements can cause diarrhoea and/or constipation and/or
      stomach cramps.


      Molybdenum

      High intakes may cause a copper
      deficiency.

      Magnesium

      Can have a powerful laxative
      effect, diarrhoea and nausea when taken in large doses


      Potassium

      In excess, may cause lethargy,
      slow heartbeat, paralysis and heart failure

      Avoid supplementing if known kidney disease


      Selenium

      Selenium toxicity can cause
      abnormal growth of toenails and fingernails, cause hair loss
      and fatigue. Intakes over more than 400µg a day need medical
      supervision


      Zinc

      High intakes can reduce copper
      absorption. Long-term use of high zinc supplements should be
      monitored. Prolonged use of high levels of zinc can cause immunosuppression.

Vitamin A
Vitamin A - retinol Supplements containing more than 600µg (2000 i.u.) should be avoided in pregnancy and by women planning pregnancy unless advised by their doctor. Vitamin A may be contraindicated in people with kidney stones or a history of kidney stones.	Vitamin A beta carotene Smokers should be advised against beta-carotene supplementation. Excess carotenes may cause the skin to become yellow (including palms of feet and soles of hands).

Vitamin C
Surplus vitamin C is excreted in the urine, but megadoses can cause stomach cramps, diarrhoea, headaches and sleep disturbances. Supplementing with more than 1000mg vitamin C is not advisable in women taking the oral contraceptive	pill (may increase oestrogen). Continued high levels of vitamin C, if suddenly stopped may produce a 'rebound scurvy', suggesting a vitamin C deficiency. This is due the body getting used to high levels and failing to adapt when levels become lower.