Are Dietary Supplements Absorbed and Are They Safe?

Our bodies need a whole host of different vitamins, minerals, and many other nutrients to function at optimal levels. We need to take in these nutrients through our diet, however, in order to get all the health supporting nutrients into our bodies, we need to have a very diverse and varied diet throughout the week.

Unfortunately, in our day and age, not all people are able to afford a varied diet or foods rich in nutrients, and some people are very short on time to concern themselves with dietary variation and nutrient intake — so people opt for dietary supplements to support their lifestyle. 

This is a very wise decision since research shows that of 19 examined micronutrients, half of the US population had deficient intakes of 6 nutrients: vitamins A, C, D, and E, calcium and magnesium and some deficiencies were found in 17 of the 19 nutrients examined. Luckily, in many Western world countries, vitamins and minerals are added to foods through enrichment and/or fortification programs. The study also found that without enrichment/ fortification and supplementation, many US citizens would not have achieved their recommended nutrient intake levels.

Luckily, statistics show that most people take at least one supplement a week. Taking dietary supplements has become part of the modern world culture, but many of us have no clue whether the supplements they consume are effectively absorbed and influence their health in a positive way. This is what I will talk about today. ed and influence our health in a positive way. This is what I will talk about today.

Supplements are available for vitamins, herbs, botanicals, minerals, enzymes, amino acids, and many other healthy products that help our bodies function well.

As we know, supplements come in many different forms including pills, tablets, powders, and drinks. Besides this variety, the combination of nutrients that supplements contain is also entirely varied, making it possible for everyone to supplement precisely the products they desire today.

This all sounds well, but are the supplements safe and useful? 

Safety of Dietary Supplements

Dietary supplements do not need approval from the US Food and Drug Administration (FDA) before they are marketed. However, supplement manufacturing companies are responsible for determining the safety and that the beneficial claims of the supplements are substantiated by adequate evidence and  are not false or misleading. The FDA is responsible for taking action against misbranded dietary supplement products after they reach the market.

In the European union supplements are considered foods and need to pass the Food Safety Act. From a safety point of view, supplements made in the US and the European Union are safe.

Most other nations have Food and Drugs Acts that also consider food supplement manufacturing and are also safe, however these should be individually examined to be on the safe side.

Usefulness of Dietary Supplements:

First of all, I wish to state the obvious and that is that it is still more than necessary to eat a health promoting diet even if you are taking the supplements you need. Supplements do not act as a substitution for food, nor are they intended to have such a function. 

But the question remains — how effective are supplements at what they’re aimed to achieve?

As a biochemist and a nutritionist, I can state that that there are certain supplements that may block the activity of other supplements, and therefore should not be taken together. On the other hand there are certain supplements that aid absorption of other supplements and therefore it is recommended to take them together. 

Here are a few examples of supplements that should not be taken together (at the same time):

  • Calcium and zinc (calcium blocks zinc absorption)
  • Calcium and iron (calcium blocks iron absorption) 
  • Calcium and copper (calcium blocks copper absorption)
  • Calcium and magnesium (certain forms of calcium block the absorption of certain forms of magnesium)
  • Calcium and vitamin D (calcium may interfere with vitamin D metabolism)
  • Zinc and selenim (zinc blocks selenium absorption)
  • Zinc and iron (zinc blocks iron absorption)
  • Vitamin B1, vitamin C and copper may hinder the absorption of vitamin B12
  • Iron and zinc (iron also blocks zinc absorption)
  • Iron and manganese (iron blocks manganese absorption)
  • Vitamin D and magnesium (vitamin D increases magnesium removal from the body)
  • Polyphenols (in grapes, wine, coffee and tea) and iron (Polyphenols block iron absorption)
  • Phytates (in whole grains, legumes, nuts and seeds) and iron (Phytates inhibit iron absorption and therefore this supplement should be taken only with fruit). 
  • Phytates and zinc (Phytates inhibit zinc absorption and therefore this supplement should be taken only with fruit or with water)
  • Phytates and manganese (Phytates inhibit manganese absorption and therefore this supplement should be taken only with fruit or water)

Here Are Some Supplements that benefit from being taken together:

  • Magnesium with B-complex (B vitamins aid magnesium absorption)
  • Zinc and vitamin A (zinc is required for vitamin A absorption)
  • Iron and vitamin C (vitamin C helps iron absorption)
  • Vitamin A and essential fatty acids (both are fat soluble and enhance absorption of the other)

For these reasons I do not recommend taking multivitamin supplements as they may actually cause nutritional deficiencies and/or nutrient excesses that are both non beneficial or may even be detrimental for health. I do however recommend food supplements which I will mention in a minute. But first I will cover the absorption of nutritional supplements.

Absorption of Dietary Supplements:

Are dietary supplements absorbed well by our body? The answer is; it depends. It depends on several factors including:

  1. The quality of the specific supplement (processing methods, additives in the supplement)
  2. The chemical structure of the nutrient
  3. Any co-administered medications
  4. The frequency of administration
  5. The levels of the nutrient in the person’s diet
  6. A persons age and gender
  7. A persons genetic profile
  8. Bacterial infection in a person

Because of the many factors influencing the absorption of certain nutrient supplements and contraindications of taking some nutrients together with others, I recommend taking food supplements rather than nutrient supplements or multivitamins. This means that the supplement taken is a whole food that is rich in nutrients rather than only specific nutrients.

Examples of these whole supe foods include Moringa, Spirulina, and Barley grass. These superfood supplements are an excellent way of providing your body with a wealth of nutrients in a balanced way as nature intended. However,  if there is a specific need for specific nutrients for certain health conditions, or for certain situations in life that require extra nutrition such as pregnancy and lactation periods, childhood, especially stressful periods and for athletes and people over the age of 50, then supplementation is ideal. 

Although I recommend food supplements, care should be taken even with these nutrient dense foods during the first 3 months of pregnancy.


If you are a healthy individual, then supplementing your diet with specific nutrient dense superfood supplements is the best and most natural way to go. If you are suffering from any health condition, then certainly specific nutrients will be of help in improving your health and vitality. Consulting with a nutritionist or doctor with an understanding in nutrition is key to preparing the right supplement regimen for you. 

If you are interested in this service, we offer a Guerrilla Diet personalized menu plan for you which includes supplement recommendations for your specific condition.  You can check it out the details here.

Feel free to comment below and let me know what you liked best about this article.

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Galit Goldfarb


[1] Charles H Halsted, Dietary supplements and functional foods: 2 sides of a coin?, The American Journal of Clinical Nutrition, Volume 77, Issue 4, April 2003, Pages 1001S–1007S, 

[2] Susanne Rautiainen, JoAnn E. Manson, Alice H. Lichtenstein & Howard D. Sesso. Dietary supplements and disease prevention — a global overview. Nature Reviews Endocrinology volume 12, pages 407–420 (2016).

[3] McRorie JW Jr. Evidence-Based Approach to Fiber Supplements and Clinically Meaningful Health Benefits, Part 1: What to Look for and How to Recommend an Effective Fiber Therapy. Nutr Today. 2015;50(2):82–89. doi:10.1097/NT.0000000000000082

[4] Ronald J. Maughan, Louise M. Burke, Jiri Dvorak, D. Enette Larson-Meyer. IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete. Volume:28 Issue: 2 Pages:104-125 doi: 10.1123/ijsnem.2018-0020.

[5] I. R. Reid  S. M. Bristow  M. J. Bolland. Calcium supplements: benefits and risks. 14 July 2015.

[6] Fulgoni VL 3rd, Keast DR, Bailey RL, Dwyer J. Foods, fortificants, and supplements: Where do Americans get their nutrients?. J Nutr. 2011;141(10):1847–1854. doi:10.3945/jn.111.142257


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