Recommended Dietary Allowances (RDA’s) – Are They Useful?

Nutrition can be a confusing subject. Let’s face it, there’s a mass of diet-related information out there, but a lot of it is very conflicting. One controversial and contentious area which has been the subject of much debate over the last few years has been the recommended dietary allowances (RDAs). Deemed to be the amount of specific nutrients required for health, we’ve been led to believe that as long as we get the RDAs for the major nutrients from our diet, then our nutritional needs will be amply covered. Against this, increasing number of scientists and nutritionists claim that the RDAs are set way too low, and that generally much higher doses are required to maintain optimum well-being. So, does taking nutrients in excess of the RDAs really offer tangible health benefits, or is it simply money down the drain?

The RDAs represent the level of nutrients needed to prevent what is known as deficiency diseases. For instance, scurvy can be prevented with just 60 mg of vitamin C each day, while a daily dose of just 1 mg of vitamin B1 can prevent the condition beri-beri. However, while an RDA represents the absolute minimum amount of a nutrient needed to prevent an obvious deficiency, it does not necessarily reflect the dose required to prevent important conditions such as heart disease and cancer. In my view, there is a world of difference between the level of a nutrient needed for basic health, and the dose required to ensure optimum health. For instance, last month in this column I wrote about research which shows that taking 100 international units (IU) of vitamin E per day seems to reduce the risk of heart attack by a third. I also described another study which showed 400-800 IU of vitamin E per day offered substantial benefits for individuals with heart disease. In the light of these findings, it does seems that taking vitamin E at the RDA level of just 14 IU is unlikely to be effective in preventing and treating Britain’s number one killer.

Another example of a nutrient for which there exists an obvious disparity between its RDA and optimal intake is vitamin C. High intakes of this vitamin have been correlated with a reduced risk of heart disease and cancer, and there is good evidence that supplementing with vitamin C can increase longevity too. More and more evidence suggests that for optimum health, each of us should be consuming at least 200 mg of vitamin C each day. What is more, during infections such as colds and flu, doses around a hundred times the RDA of 60 mg may be required to speed recovery and restore health.

While the RDAs for certain nutrients do indeed appear to be set too low, for many nutrients, no RDA exists at all. It is known that we require about 50 different nutrients to sustain life. Looking more closely at the nutrients with no official RDA level, it does seem as though there has been some glaring omissions. A good example is the antioxidant mineral selenium. A study published in the New England Journal of Medicine in 1996 showed that supplementing with selenium at a dose of 200 mcg per day effectively halved an individual’s risk of dying from cancer. And yet, to this day, no RDA for selenium exists. Other key nutrients for which no RDA exists include beta-carotene (another important antioxidant), chromium (thought to help reduce the risk of diabetes), copper (important for soft tissue formation and the maintenance of healthy cholesterol levels).

One major failing of RDA system is that it does not take account of a person’s individual nutrient requirements. Over the last two decades there has been growing interest in a nutritional concept known as ‘biochemical individuality’. The idea here is that individuals may not necessarily have the same nutritional needs. For example, the calcium requirements of a middle-aged woman may not be the same as a 20-year-old man. The fact is, the amount of a nutrient an individual requires for health is affected by many different factors including genetic make-up, sex, age, levels of stress, activity levels, alcohol consumption, pollution, smoking, the use of prescription medications, pregnancy and menopause. Apart from making occasional and minor distinctions between the sexes, the RDAs simply make no provision for the special requirements individuals may have for nutrients.

One of the things which causes resistance to taking nutrients in doses which exceed the RDAs is a feeling that doing so may lead to problems with overdose and toxicity. For the most part, this is simply not the case. The RDAs are not intended to reflect the safe levels of nutrients at all. There is now a wealth of scientific literature designed to determine the levels of nutrients safe for human consumption. Generally, what we find is that the safe daily intake for a nutrient is many times the RDA. For instance, while the RDA for vitamin B6 is just 2 mg, there is good evidence that suggests its upper safe limit is at least 200 mg. Disappointingly, and despite good evidence science to the contrary, the European Union body responsible for determining safe levels of nutrients (the Scientific Committee on Food) has recently recommended that vitamin B6 be subject to an upper safe limit of 25 mg per day.

There seems little doubt that the RDAs are outdated, inappropriate, and well overdue for review. Personally, I don’t give the RDAs a second thought. My feeling is that more emphasis should be placed on the real doses of nutrients required for optimum health. There is now a wealth of scientific and anecdotal evidence which supports the idea that taking nutrients in excess of the RDA can be a safe and effective way to enhance health and prevent illness.


  1. low carbohydrate - 25 September 2009

    low carbohydrate…

    Your topic Vidyya Research Rounds Podcast ” Blog Archive ” Low Carb … was interesting when I found it on Friday searching for low carbohydrate…

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