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Sometimes Less is More - Nutritional Reference Values

When it comes to nutrients many people may be familiar with the term RDA – or Recommended Daily Amount. However, in 2014 this was changed to Nutrient Reference Value (NRV)...

When it comes to nutrients many people may be familiar with the term RDA – or Recommended Daily Amount. However, in 2014 this was changed to Nutrient Reference Value (NRV) for most nutrients. The exceptions are calories, protein, fat and carbohydrates where RDAs are still used. The values for the NRVs are the same as RDAs. It’s just the terminology that has changed. Some sources use the term Daily Reference Values or DRVs but we will use NRVs here.

NRVs are recommendations based on the most up to date scientific knowledge. They state how much of the essential nutrients are needed to meet the nutritional needs of most people.

How Much is Too Much?

Whilst nutritional recommendations are given on a population level it is likely that we all have different needs and that these needs will vary over time depending on diet, exercise, stress, season, and life stage.

In the same way that eating too much food is not good for you, taking mega doses of nutrients from supplements is also unlikely to be helpful and may be harmful. Your body can’t utilise more than it needs. Excess of anything puts a strain on the system and has to be stored or eliminated.

Nutrients work synergistically. Taking a large dose of one or two nutrients causes an imbalance leading to less efficient body function.

Side Effects

Side effects of overdosing on nutritional supplements vary but here are a few:

  • Excess vitamin C may cause diarrhoea, stomach cramps and bloating.
  • Overdosing on B vitamins may lead to insomnia and nervousness.
  • Folic acid (one of the B vitamins) is added to many foods. It is a vital nutrient for preventing birth defects. However, taking in too much can mask the signs of vitamin B12 deficiency, which may lead to permanent nerve damage if left untreated, especially in the elderly.

That said, the B vitamins and vitamin C are water soluble so excess amounts are generally passed out in the urine.

More dangerous are the non water soluble nutrients that can build up in the body.

  • Too much selenium can lead to hair loss and mild nerve damage.
  • Regularly consuming more than the recommended levels of vitamin D can lead to serious heart problems.
  • Vitamin A or retinol is not water soluble so is stored in the liver. In excess it can damage the liver, cause birth defects, and might harm the bones.
  • Even one large dose of iron can damage the liver and negatively affect the central nervous system. Iron is not easily excreted so should only be taken if there is a diagnosed deficiency.
  • Regular users of calcium supplements have an increased risk of having a heart-attack compared to those who don’t take calcium. Calcium needs co-factors such as vitamin D3, K2, magnesium and boron in order to be absorbed into the bones and used appropriately by the body. Without these co-factors calcium can be deposited on the arteries leading to atherosclerosis, or can build up to form kidney stones.

Supplements to Supplement Your Diet

The majority of your nutrients should come from your food. That said, with depleted soils and less than optimum diets there are likely to be times when taking supplements is extremely valuable. But supplements should be just that, a supplement to a healthy diet, not your main source of nutrients.

When buying or taking supplements, check the labels for how much of each nutrient is in the product compared to the NRV. It’s best to take the smallest dose that makes a difference. Start with a small dose and build up gradually if you feel more is needed.

The current NRVs for adults are listed below. These vary according to age, gender and life stage but this can be used as a guide.



Nutritional Reference Value

Safe upper limit





Vitamin A

3,000 IU 900 µg

2,300 IU 690 µg

10,000 IU

Niacin (B3)

16 mg

14 mg

35 mg

Folate (folic acid)

400 µg

400 µg

1,000 µg

Vitamin C

90 mg

75 mg

2,000 mg

Vitamin D

600 IU/15µg ages 19 to 70

800 IU/20µg ages 71 and up

600 IU/µg ages 19 to 70

800 IU/20µg ages 71 and up


Vitamin E

22 IU/14500 µg (natural)
33 IU/30000 µg (synthetic)

22 IU (natural)/14500 µg
33 IU/30000 µg (synthetic)

1,500 IU (natural)
1,100 IU (synthetic)

Vitamin K

120 µg

90 µg

Not established







1,000 mg ages 19 -70

1,200 mg ages 70 +

1,000 mg age 19 - 50

1,200 mg ages 51 +

2,500 mg up to age 50

2,000 mg ages 51 +


420 mg

320 mg

350 mg (from supplements only)


4,700 mg

4,700 mg

Not established


55 µg

55 µg

400 µg


11 mg

8 mg

40 mg

Source: Institute of Medicine and the Office of Dietary Supplements, National Institutes of Health.

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