Dangers of some food supplements- Interactions with foods and medicines- CYP3A4 enzyme

Photo by Polina Tankilevitch from Pexels

Many people believe when they see the word natural, its okay to take as much as they want since its ‘found’ in nature. However ‘natural’ products can be very dangerous.

One interaction most people are aware of is with grapefruit, this is seen as a warning on many prescription packets. Grapefruit juice affects how drugs are changed (metabolised) in the body for eventual elimination and can alter the amount of drug in your blood. This can lead to enhanced side effects or lower drug effectiveness. Drugs or toxins are usually broken down (metabolised) so that they can be eliminated from the body, and they pass through the liver. Grapefruit or grapefruit juice can alter enzymes in the body and affect how drugs are changed in the body before they are eliminated. In the case of grapefruit it decreases the activity of the cytochrome P450 3A4 (CYP3A4) enzymes that are responsible for breaking down many drugs and toxins.

Grapefruit contains compounds known as furanocoumarins that block the CYP3A4 enzymes. When grapefruit juice is consumed, the enzyme’s ability to break down the drug for elimination is decreased. Blood levels of the drug may rise, resulting in a risk for new or worsened side effects. Blood levels of the drug may rise, resulting in a risk for new or worsened side effects. One whole fruit or 200 milliliters of grapefruit juice (a bit less than one cup) can block the CYP3A4 enzymes and lead to toxic blood levels of a drug. (1)

Taking medications at a different time from when grapefruit juice is consumed may not prevent the interaction. The effects of grapefruit juice on certain medications can last for over 24 hours. So, even if you take a medicine that is given only once per day, grapefruit and grapefruit juice should still be avoided for the entire treatment period.

Most worryingly Susan sees on some sites that its okay to take certain supplements two hours after any prescription medication or four hours after a medication that says do not take with grapefruit juice, since the supplement uses the same CYP3A4 pathway. There is no evidence to support this, there are a variety of factors that affect how a drug is metabolised (2). Some interactions can inhibit or change the rate its metabolised, while it may not have much effect on you if your hayfever medication is affected, it could have more serious consequences if its your Contraception, Epilepsy or Blood Pressure medication is affected.

Photo by Nataliya Vaitkevich from Pexels

Other CYP enzymes are also affected, in particular the following foods often found in supplements can have an interaction:-

  • Gingko
  • Grape Seed Extract
  • Liquorice
  • Milk Thistle
  • Echinacea
  • Garlic
  • Ginger
  • Ginseng
  • Piperine
  • Pomegranate
  • Quercetin
  • St John’s Wort
  • Berberine
  • CBD oil
  • Chamomile
  • Cranberry
  • Curcumin

The CYP enzyme system is responsible for the metabolism of 90% of prescribed drugs and herbs can induce or inhibit the CYP enzymes. Medication, toxins and hormones are all processed through the liver and some have more than one pass (3), this varies from drug to drug which is why there is no general rule of when it’s safe to take a product that interacts. In particular as you age your liver metabolism slows down so the risk increases (4), quite often more side effects are seen and then more drugs are prescribed to counteract the side effects.

Susan carries out a drug interaction assessment with every client having a full review to ensure that any current self medicated supplements are safe , and any prescribed supplements are suitable.

  1. accessed 24th July 2021

2. 24th July 2021

3. accessed 24th July 2021

4. accessed 24th July 2021



For many of Susan’s clients they show symptoms of magnesium deficiency, unfortunately because serum magnesium does not reflect intracellular magnesium, the latter making up more than 99% of total body magnesium, most cases of magnesium deficiency are undiagnosed. In developed countries it has been found that just over 24% of youth have insufficient magnesium in their diets. The RDA for magnesium is between 300mg – 420mg per day.  It is estimated that less than 50% of Americans hit the recommended daily amount.  Magnesium deficiency has been found in 84% of postmenopausal women with osteoporosis.
Since 1940 there has been a tremendous decline in the micronutrient density of foods. In the UK for example, there has been loss of magnesium in beef (−4 to −8%), bacon (−18%), chicken (−4%), cheddar cheese (−38%), parmesan cheese (−70%), whole milk (−21%) and vegetables (−24%).The loss of magnesium during food refining/processing is significant: white flour (−82%), polished rice (−83%), starch (−97%) and white sugar (−99%).
Increased calcium and phosphorus (cola in particular is a large source of some individuals phosphorus intake)  intake also increases magnesium requirements and may worsen or precipitate magnesium deficiency.
A common misconception is that consuming phytate-rich foods can lead to nutrient deficiencies particularly magnesium depletion via binding by phytic acid. However, urinary magnesium excretion will drop to compensate for a reduction in bioavailable magnesium. And most high-phytate foods are also good sources of magnesium (grains and beans are good examples). Thus, it is unlikely that consuming foods high in phytate will lead to magnesium depletion. However, a vitamin B6-deficient diet can lead to a negative magnesium balance via increased magnesium excretion.
The reasons for magnesium deficiency are varied, some are dietary and since most vitamins and minerals work in synergy with each other they all must be balanced,

supplementing with calcium can lead to magnesium deficiency due to competitive inhibition for absorption and over supplementing with vitamin D may lead to magnesium deficiency via excessive calcium absorption. Use of diuretics and other medications can also lead to magnesium deficiency.

Kidney failure, alcohol consumption and absorption issues  (Magnesium is absorbed in the small intestine and colon)  also effect magnesium levels. Thus, individuals with intestinal or colon damage such as Crohn’s disease, irritable bowel syndrome, coeliac disease, gastroenteritis, idiopathic steatorrhoea, ulcerative colitis, resection of the small intestine, ileostomy patients or patients with ulcerative colitis may have magnesium deficiency.

So what are the best  dietary sources:-
Black beans
Dark Chocolate
Kidney beans
Peanut butter
Unrefriend Whole grains
Dietary sources are always the optimal way of obtaining your nutrients.

Choose your supplements wisely

Bio-availability refers to the bodies ability to absorb and use a particular substance or nutrient.

Vitamins and minerals are manufactured from either ‘organic’ or ‘inorganic’ materials.  Minerals in the form of sulphates, oxides, carbonates or artificial chelates are  inorganic, meaning they  rarely occur naturally in the plant or animal kingdoms.  Minerals in the form of  gluconates, phosphates, citrates, lactates are called ‘organic’ minerals because they do occur in  the plant and animal kingdoms.  Organic mineral forms are believed to be absorbed  easier by the body.


One example can be seen in the supplement calcium, in 1987 Maryland University carried out a study to investigate the different forms of calcium  and absorption since it already had been determined that the solubility of many calcium salts, depends on pH, the type of salt used, the condition of the patient and the time of administration.

Previously it was assumed that all calcium supplements were equal, as long as the amount of calcium in each supplement was the same, however it was found that calcium must be in the form of ions to be absorbed. As with many salts the solubility depends upon the pH of the solution its dissolving in.  To be of use in the body first the tablet must disintegrate, It was found that some tablets had coatings on “enteric-coated” that were insoluble in acid, these coatings are of use to other supplements where the disintegration is needed further down the digestion track, or packed too tightly together ‘bed pan bullets’  (The standard laboratory test for disintegration (part of the test known as the United States Pharmacopeia [USP] “Disintegration and Dissolution of Dietary Supplements” method <2040>), is an important test of product quality, although passing this test alone does not assure bioavailability). The research also found that calcium carbonate and calcium phosphate dissolved well at a pH of 1.01(very acidic) but their solubility reduced as pH increased, the average stomach acid  pH of a human is 1.5-3.5, therefore for bioavailability calcium citrate and calcium lactate are better forms.

Susan has a practitioner account with Natural Dispensary where she can offer her clients a 10% discount off their price list.   If you want to discuss any of your supplements, please contact Susan.






Better You Products

Better You products are popular with many being in a convenient spray form.

Vitamin D

Essential for calcium absorption, maintaining healthy bones and teeth, supporting a healthy immune system and contributing to normal muscle function.  Vitamin D is recommended in the UK for many individuals, during the winter months.

Vitamin B12

Vitamin B12 is a notoriously difficult to absorb through diet alone for many individuals. It is essential to support cognitive function and plays an important role in ensuring healthy red blood cell formation, proven to help reduce tiredness and fatigue.

Vegans often need to supplement B12 if not consuming fortified products.


Very popular with runners to help their muscles after a run and for individuals with restless legs.


Note: Information on products does not constitute advice, if you require personal recommendations on products and dosages please make an appointment with Susan.