Registered Nutritionist Sarah Dumont-Gale explains why some supplements contain more or less of a nutrient's Nutrient Reference Value (NRV), and what this means for your nutrient intake.
NRV, or Nutrient Reference Value, replaced the older term RDA (Recommended Daily Allowance). If you use supplements alongside a healthy lifestyle to improve your health, you may be familiar with the term, which shows how much of your recommended daily intake of a nutrient is in a certain supplement. But why do some supplements contain more or less of this guideline amount?
What does NRV stand for?
NRV stands for Nutrient Reference Value. This is the level of a nutrient that is considered adequate to meet the nutritional requirements of an average healthy adult to prevent deficiency. NRVs are set for vitamins and minerals for the purpose of food labelling based on European food legislation, and there is only one NRV for each nutrient. Food supplement labels list the quantity of a nutrient in the product alongside the percentage of the NRV value: for example, 80mg vitamin C providing 100% NRV.
Where it can start to get confusing is that different areas of the world may have defined their own NRV (or the equivalent term). This is typically because our climates, diet and lifestyles differ globally, but also because different criteria were used to define the values. For example, the US uses Daily Values (DV), which up until early 2020 were based on outdated recommendations from almost 50 years ago. Find out about the differences between RDA, NRV, RNI and other nutrient intake measurements in this article.
Can we always reach our recommended intake through food?
The NRV is set for the purposes of food labelling and use in supplements, but we of course also take in nutrients through non-packaged, fresh produce. Unfortunately, it's hard to reach our NRV for some nutrients even with a balanced diet.
In the UK, the prevalence of vitamin B12 deficiency is around 6% in people aged under 60 and rises to 20% for individuals aged 60 and over, which is likely due to absorption reducing as we age.2 Plant-based diets are also a contributing factor in vitamin B12 deficiency, as there are no sufficient plant-based sources.
Vitamin D is another nutrient where we should not rely on food sources alone to meet our nutritional requirements. Living in the UK means we do not get sufficient sunlight exposure during the winter months to produce adequate vitamin D, and as advised by the National Institute for Health and Care Excellence (NICE) we should all be supplementing with 10mcg vitamin D during autumn and winter.
What's more, vitamin C cannot be produced by the human body. Humans are one of the only mammals, including Guinea pigs, that cannot manufacture vitamin C themselves. This is why it is essential we either focus on getting vitamin C through our diets, including lots of colourful fruits and vegetables, or by taking a supplement.
The humble orange is often thought to contain the most vitamin C, but gram for gram red bell peppers actually contain more. The NRV for vitamin C is set quite low at 80mg, whereas it is thought by many experts that 500mg or 1g is a more optimal level to meet our nutritional needs.
Why do some supplements have more than 100% NRV?
Everyone has their own unique, individual need for each vitamin and mineral, and this will depend on a multitude of factors such as age, weight, gender, level of activity and genes inherited. Some individuals will require less, while others may require more, and it is impossible to set population guidelines that consider these personalised factors.
The NRV should be used as a guide to help prevent deficiency, but the levels may not be suitable for optimal health. For example, it has been determined that the average healthy adult requires 5mcg of vitamin D per day to prevent vitamin D deficiency and the development of rickets. This level was recommended based on the old understanding that vitamin D was only used for calcium absorption to maintain healthy bones.
We now understand that vitamin D plays a larger role in health and plays a beneficial role in many other mechanisms in the body.1 The National Institute for Health and Care Excellence (NICE) advises that everyone from the age of one year should take a supplement supplying 10mcg vitamin D during autumn and winter (see box above).
However, this amount is very much the minimum. Many experts now suggest that, in the absence of exposure to sunlight, an intake of 25mcg (1000iu) is more appropriate for optimum heart, brain and immune health. A higher intake of at least 50mcg vitamin D3 may be more appropriate for older people, to offset lower production in the skin and because of reduced dietary absorption.
Why do some supplements have less than 100% NRV?
NRV is set at the level required for daily consumption, so it is important to consider total daily intake across multiple supplements and not just how much of a nutrient each supplement provides in isolation.
Safe Upper Limit (SUL)
Some vitamins and minerals have also had a Safe Upper Limit (SUL) set. SUL defines an intake of vitamins and minerals that, on the basis of the available evidence, can be consumed over a lifetime without significant risk to health. The Expert Group on Vitamins and Minerals has set SULs for 8 vitamins and minerals, and guidance was issued for 22.3
As an example, the SUL for zinc is set at 25mg per day. If you were taking a multivitamin plus another two products all containing 100% NRV zinc, then you would be over the SUL. This is known as vitamin stacking, and careful consideration is put into the formulations of multi-nutrient supplements to help prevent this. It is advisable to always stay below the SUL to be confident that no harm should occur from a daily intake up to that level.
Another reason why a supplement's NRV may be below 100% is because sometimes it is difficult to fit the full NRV into one tablet without it becoming unswallowable, especially if it is a multivitamin. Often, there will be lower levels of magnesium and calcium in multi-nutrient products, as both these minerals need to be bound to another substance before being tableted.
For example, magnesium is a very chemically active element, and magnesium supplements will utilise magnesium citrate, a form of magnesium bound to citric acid, or magnesium oxide, which is a salt that combines magnesium and oxygen.
These compounds can be quite large, so to be able to provide a tablet that is comfortable enough to swallow, either a lower NRV is used, or more than one tablet is advised as the daily dose.
Looking beyond NRV
The NRV should be used as a guide to help prevent deficiency, but there is no need for alarm if the percentage NRV on a supplement is under or over 100. Eating a broad, varied, and balanced diet is the best foundation to improve your health, and if you are supplementing, check you are not vitamin stacking and have a look at the SUL guidance.
Finally, if you have a particular health concern, it may be worth looking beyond the NRV and investigating what your personal requirements for that nutrient should be for optimal health.