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Nutritional Requirements

How Much of a nutrient is enough?

There is a lot of official and semi-official guidance on this question. There are Recommended Daily Allowances (RDAs), Recommended Daily Intakes (RDIs) Reference Nutrient Intakes (RNIs) and Upper Safe Limits (USL). All of these define a position on the above question. The first three are official attempts to advise everyone on the least amount of each nutrient needed to avoid deficiency. The third one (USL) seeks to answer quite a different question, which is “how much is it safe to have?” This last question is posed and answered irrespective of any estimate of how much is needed.

Usually anyone interested in using supplements to maintain or improve health wants a simple answer to the question, “How much should I have?” Unfortunately the answer is not so simple because one needs to take account of individual variation, age and sex and one needs to define what you actually mean by “deficiency”, “maintain” and “improve”. You have to take many more unknown factors into account, such as how much you smoke or drink or how much tea or coffee you consume. You may also need to consider, when dealing with one nutrient, how much you are taking of certain other nutrients. Taking one may depress or enhance the absorption or utilization of another. Then again, not only tea and coffee, but also some foods act as inhibitors of the absorption of some nutrients. The more of these foods you take the higher the intake of the nutrients needed to avoid running short of them.

You cannot have all of these factors evaluated carefully without a very detailed professional assessment. Therefore, all the attempts to evaluate “need” take a broad-brush approach that rides roughshod over the individual differences.

A very important landmark in estimating nutritional requirements in the UK was the publication by HSMO in 1991 of a report of the Panel on Dietary Reference Values. This was a sophistication of previous methods in that the Panel recognised that the average requirements across the whole population failed to meet the needs of those people whose needs were above the average. The average values were listed in the report and were called “Estimated Average Requirements” (EARs). However, the Panel produced a much more useful value called “Reference Nutrient Intake” or RNI. This was defined as “an amount of the nutrient that is enough, or more than enough, for about 97% of people in a group. Whilst this may seem reasonably fair, it really does not help if you happen to be one of the 3% whose needs are not met by this level of nutrition.

The Panel on Dietary Reference Values, in its wisdom, wrote, “If average intake of a group is at the RNI, then the risk of deficiency in the group is very small”. We do not consider that the Panel was necessarily correct here. For this to be true the distribution of intake within the group must be even or nearly so. In point of fact, where you have a population depending upon the diet for supply of nutrients, if the nutrient is very unevenly distributed among members of the population, then there will always be an “underclass” of people who can be quite markedly deficient. This certainly happens in the UK. Where the average intake of a nutrient is very close to the recommended value or just below it (as in the case of magnesium), the distribution is very uneven, depending upon the diets of different individuals or groups, and hence a whole swathe of the population receives intakes at deficiency or sub-clinical deficiency levels.

Therefore, even if we go no further than to consider the avoidance of deficiency, the RNI may not be sufficient, when applied to groups or populations. When applied to an individual, in the admission of the Panel, there is still a 3% chance of being deficient. It is hard lines if you are one of those people.

The RDA and the RDI were earlier attempts to define requirements. These recommendations would keep the majority of the population away from deficiency, but they suffered from the same limitations as RNI.

However, when we are dealing with any of these official figures we are limiting ourselves to trying to avoid deficiency. Being deficient means, to most orthodox nutritionists, having the symptoms of specific deficiency diseases that are associated with many of the individual nutrients. Thus, these recommendations, if we adhere to them, will protect the majority of people from beriberi (in the case of Vitamin B1) or scurvy (in the case of Vitamin C). Sometimes rather more sophisticated biochemical criteria have been used, like in the case of selenium, where the selenium content of a selenium-requiring enzyme has been used as a yardstick.

This is a rather cheeseparing approach to nutrition by which, it often seems, and the government body ends up recommending us as little as possible. As a result, the official recommendations have been reducing over the years. Zinc is a good example. In 1991 the Panel produced an RNI of 9.9mg/d for adult men and 7.0mg/d for adult women. Previously, the USA had arrived at a figure of 15mg/d, which had been widely followed in the UK. In the mean time the zinc content of agricultural crops in the UK had fallen markedly to values that made it hard to obtain from foods much more zinc than the Panel’s new recommendations. The Panel looks independent enough but one sometimes wonders whether the recommendations are being massaged downwards to match the amount that the average person can obtain in food. For all these reasons there is little confidence these days amongst nutritionists, especially alternative nutritionists, that these official recommendations are sufficient to provide the best protection against development of chronic illness in the long term. There is no disagreement that they do protect from deficiency symptoms in the shorter term.

Next one needs to consider a strategy for supplementation. One very common one is to take the RNI amount as a supplement. Since, you have the nutrients in your diet as well, you will be assured that your intake will then be well in excess of the RNI because you have the supplement intake plus the intake in food. That strategy will almost certainly protect against overt deficiency symptoms. But the real question is “How much protection do you want?” If you want even more certain and more thorough protection then you might consider taking twice the RNI.

Then again you can look at particular strategies for different nutrients. In the case of selenium, the UK 1991 RNI values are 60 micrograms (mcg) for a woman and 75 mcg for a man. Yet a strong case can be made for a supplement of 100mcg/d, especially with advancing years, to help to minimise the risk of cancer. Some consider that 200mcg/d should be used, and a few experts even advise 300mcg. Here we hit a very real controversy in nutritional circles between the “orthodox” and “alternative” views. There much evidence that levels of nutrients considerably higher than the RNIs can provide health benefits over and above preventing the signs and symptoms of overt nutrient deficiency syndromes. Yet the Panel on Dietary Reference Values purposely ignored all such evidence and concentrated only on the avoidance of deficiencies. So we must ask, “What is a deficiency?” Is it just enough to avoid an obvious deficiency illness (in the case of selenium this might be Keshan disease) or is it enough to provide really good health and function and relative freedom from acquired chronic illnesses as the years pass?

This inevitably brings us to the Upper Safe Limit because if we increase the intake too much we may encounter overdosing effects with a few of the nutrients. Selenium is a good example. There comes a point at which the increasing intakes cease to give any further benefit and eventually there might be adverse results. It is important to know what these levels are. In the case of selenium estimates of the start of the adverse level vary between 750mcg and 3200mcg so these levels probably should not be used. The Panel on Dietary Reference Values suggested that they did not feel confident of the safety of selenium above 450mcg/d so this is their USL. This is a reasonable figure. Other sources have arrived at different values. This is understandable because this is a matter of professional judgement rather than an absolute measurement. Sometimes these estimates come down far too close to the RNI, in which case we may think that excessive caution is being applied and that the public is then being deprived of beneficial levels of supplement. We note that, notwithstanding the 450mcg level suggested above, up to 1000mcg was used in China in reversing the selenium deficiency of Keshan disease, apparently without adverse effect.

In the case of selenium there are different chemical forms that can be used in supplements. The main difference is between inorganic sodium selenite and the organic forms such as selenocysteine, selenomethionine or selenium yeast. The evidence indicates that organic forms are both more effective per mcg used and also safer at higher intakes than the inorganic form. This should have an effect upon the RNI and the USL but this important factor is usually omitted from official recommendations.

We have said little here about the RDAs. This is because they were replaced in the UK by the RNIs in 1991. However, European recommendations still use the abbreviation RDA. Although these values are not quite the same as the UK RNIs most of what we have said here about RNI also applies to the European RDAs.

We think that when you are looking at nutritional supplements across the board it is reasonable to apply the factor 1.5 times the RNI. When you are looking at individual nutrients that may be taken for specific benefits quoted in the literature one may need higher values to gain the claimed benefits. This is true of Vitamin C, where at least 1000mg/d may be suggested in literature references but the RNI is just 40mg for both men and women. Intakes of 1000mg, being 25 x the RNI, are controversial. They are generally frowned upon by orthodoxy but favoured by alternative medicine sources. The value of the publicised USL, and the desirable chemical form of the nutrient are then important and the matter is not fully settled.

Similarly, there are a number of nutrients for which there is no RNI. Chromium is one such example. The Panel on Dietary Reference Values nonetheless suggested that 25mcg/d would be enough for adults. Yet one has noted distinct benefits from using 200mcg/d and the literature reports up to 400mcg as being necessary for weight reduction and increase in lean body mass. Again, with chromium, different chemical forms behave differently and one needs to be aware of this variable.

Finally, there are many nutrients, especially phytonutrients, that are not considered essential but which are enormously beneficial. In these cases one gets no official help or advice and no RDAs, RNIs or USLs apply. Carotenoids and flavonoids are examples of these. The intake of these is very protective of our health but one can only go on recommendations from suppliers, nutritional experts or literature suggestions.

TABLE A

Vitamins Recommended Daily Allowance

Vitamin A

800 µg

Vitamin D

5 µg

Vitamin E

12 mg

Vitamin K

75 µg

Vitamin C

80mg

Thiamin

1.1 mg

Riboflavin

1.4 mg

Niacin

16 mg

Vitamin B6

1.4 mg

Folic acid

200 µg

Vitamin B12

2.5 µg

Biotin

50 µg

Pantothenic acid

6 mg

TABLE B

Minerals Recommended Daily Allowance

Potassium

2000 mg

Chloride

800 mg

Calcium

800 mg

Phosphorus

700 mg

Magnesium

375 mg

Iron

14 mg

Zinc

10 mg

Copper

1 mg

Manganese

2 mg

Fluoride

3.5 mg

Selenium

55 µg

Chromium

40 µg

Molybdenum

50 µg

Iodine

150 µg

(Ref: FLR, Schedule 6, Part II Ammend)

Food Labelling Nutrition Information, Regulations 2009, EC Directive 2008/100/EC(amending 90/496/EC)

In force from 30th October 2009; trade in products not complying prohibited from 31st October 2012

N.B. Source claims can only be made if the daily intake provides at least one-sixth of the RDA of the named vitamin or mineral.

Optimal and RNI levels for vitamins:

NUTRIENT CHEMICAL FORM AND OR UNITS RNI (MALE) “OPTIMUM” RNI (FEMALE) “OPTIMUM”

Vitamin A

mcg retinol equivalent

700
None needed when in good health if sufficient beta-carotene

1050
None needed when in good health if sufficient beta-carotene

600
None needed when in good health if sufficient beta-carotene

900 (except in pregnancy)
None needed when in good health if sufficient beta-carotene

Beta-carotene

Beta-carotene, (mcg) preferably natural origin accompanied by some alpha carotene and some other carotenoids

No RNI - 4200 would equate to the RNI for Vitamin A

6300 would apply if there was no Vitamin A intake

No RNI - 3600 would equate to the RNI for Vitamin A

5400 would apply if there was no Vitamin A intake

Thiamin (Vitamin B1)

mg

0.4

0.6

0.4

0.6

Riboflavin (Vitamin B2)

mg

1.2

1.8

1.1

1.65

Niacin (Vitamin B3)

mg nicotinic acid or nicotinamide

6.6
Note dependence upon tryptophan intake

10
Note dependence upon tryptophan intake

6.6
Note dependence upon tryptophan intake

10
Note dependence upon tryptophan intake

Vitamin B6

mcg pyridoxal, pyridoxine or pyridoxamine per g of protein intake

15
Note value depends upon intake of protein – averages 1.05mg/day

22.5
Note value depends upon intake of protein – averages 1.6mg/day

15
Note value depends upon intake of protein – averages 1.05mg/day

22.5
Note value depends upon intake of protein – averages 1.6mg/day

Vitamin B12

Different forms of cobalamine (mcg)

 

1.2

4

1.2

4

Folate

Pteroyl glutamic acid and its glutamyl conjugates or tetrahydrofolate in foods (mcg)

200

400

200

400

Pantothenic acid (Vitamin B5)

No RNI (mg)

3-7 regarded as normal

20

3-7 regarded as normal

20

Biotin

No RNI (mcg)

10 – 200 regarded as “safe”

200

10 – 200 regarded as “safe”

200

Vitamin C

Ascorbic acid (mg)

40

250

40

250

Vitamin D

Cholecalciferol or ergocalciferol (mcg)

Zero to age 50, then 10 but depends upon adequate sunlight exposure

Zero to age 50, then 10 but depends upon adequate sunlight exposure

Zero to age 50, then 10 but depends upon adequate sunlight exposure

Zero to age 50, then 10 but depends upon adequate sunlight exposure

Vitamin E

Tocopherols and tocotrienols – alpha tocopherol used as reference – no RNI

7mg suggested but depends upon intake of unsaturated fatty acids

100

5mg suggested but depends upon intake of unsaturated fatty acids

100

Vitamin K

Phylloquinone (mcg)

1 mcg per kg body weight suggested – average about 70mcg

100mcg

1 mcg per kg body weight suggested – average about 70mcg

100mcg

Optimual and RNI levels for minerals, please note that all levels are given as “elemental weights”:

NUTRIENT CHEMICAL FORM AND OR UNITS RNI (MALE “OPTIMUM” RNI (FEMALE) “OPTIMUM”

Calcium

Calcium salt of a non-toxic organic acid (mg)

700

700 – note UK dietary intake is mainly satisfactory and there may be no supplementation needed

700

700 – note UK dietary intake is mainly satisfactory and there may be no supplementation needed

Magnesium

Magnesium salt of a non-toxic organic acid (mg)

300

400

270

360

Iron

Ferrous salt of a non-toxic organic acid (mg)

8.7

10 – note UK dietary intake for many men is satisfactory and there may be no supplementation needed

14.8

16 – note UK dietary intake is often unsatisfactory and supplementation is often needed in pre-menopausal women

Zinc

Zinc salt of a non-toxic organic acid (mg)

7

15 – the UK RNI may well be an under-estimate and falls well below the USA estimate

7

15 – the UK RNI may well be an under-estimate and falls well below the USA estimate

Manganese

Manganous salt of a non-toxic organic acid (mg)

No RNI but ‘above 1.4mg/day recommended by panel

7 – there is a suspicion that lack of information has led to under-estimation of official figures

No RNI but ‘above 1.4mg/day recommended by panel

7 – there is a suspicion that lack of information has led to under-estimation of official figures

Molybdenum

Molybdates (mcg)

No RNI but panel recommended 50 – 400 mcg

150

No RNI but panel recommended 50 – 400 mcg

150

Chromium

Must be trivalent, never hexavalent (mcg), preferably organic, GTF form is by far the best (mcg)

No RNI but panel recommended ‘above 25mcg’

100

No RNI but panel recommended ‘above 25mcg’

100

Iodine

Potassium iodide (mcg)

140

140

140

140

Selenium

Selenomethionine or selenium yeast but only sodium selenite (which is more toxic) is on approved list (mcg)

75

150 – there is plenty of evidence of added protection at higher intakes

60

120 – there is plenty of evidence of added protection at higher intakes

Copper

Copper salt of non-toxic organic acid (mg)

1.2

2

1.2

2

Silica

Much Si in the diet is silica but for absorption a soluble form is needed like silicates or silicic acid (mg)

No RNI – UK study reported that intake of 1200 is normal

There is reason to suspect that intakes of absorbable silicon are low, hence extra 75mg of absorbable form may be beneficial

No RNI – UK study reported that intake of 1200 is normal

There is reason to suspect that intakes of absorbable silicon are low, hence extra 75mg of absorbable form may be beneficial

Boron

Boric acid or borate (mg)

None

Possibly none needed

None

2 suggested to maintain bone density, especially in menopausal and post-menopausal women but not on approved list

Table 1:
A comparison of the current HFMA Nutrient Daily Upper Safe Levels (USL) for Supplementation with the daily levels for supplementation proposed by the Food Standards Agency Expert Group on Vitamins and Minerals (EVM) and the USLs for TOTAL DAILY INTAKE from the US Food and Nutrition Board (FNB) and the EU Scientific Committee for Food (SCF).

Nutrient Unit HFMA USL - daily† EVM SUL
(proposed) - long-term*
FNB
Total intake
USL
SCF
Total intake USL
as of March 2003

Vitamin A

µg

2300

1500 (G, T)

3000

3000

Beta-carotene

mg

20

7

Not recommended

No conclusion

Vitamin D

µg

10

25 (G)

50

50

Vitamin E**

mg

800

540 (800 IU)

1000

Not yet reviewed

Vitamin K

µg

1000 (G)

No limit set

Not yet reviewed

Thiamin (B1)

mg

100

100 (G)

No limit set

No limit set

Riboflavin (B2)

mg

200

40 (G) (43T)

No limit set

No limit set

Nicotinamide

Nicotinic acid

mg

mg

450

150

500 (G) (560T)

17

35 as supplement+ diet

900

10

Pyridoxine (B6)

mg

200

200 (short term)†††
10 (long term)

100

25

Vitamin B12

µg

500

2000 (G)

No limit set

No limit set

Folic acid

µg

400

1000 (G) (1500T)

1000 supp.
(+200 diet)

1000

Biotin

µg

500

900 (G) S (970T)

No limit set

Not yet reviewed

Pantothenic acid

mg

500

200 (G) (210T)

No limit set

No limit set

Vitamin C

mg

2000

1000 (G)

2000

 

 

 

 

 

 

 

Calcium

mg

1500

1500 (G)

2500

Not yet reviewed

Phosphorus

mg

1500

250 (G) (2400T)

 

Not yet reviewed

Magnesium

mg

350

400 (G)

350 as supplement+ diet

250 as supplement

 

 

 

 

 

 

Boron

mg

Not reviewed

6 (9.6T)

20

Not yet reviewed

Chromium (trivalent)***

mg

0.2

10 (G, T)

Insufficient data
No recommendation

Not yet reviewed

Cobalt

μg

Not reviewed

4. 6 (G, T)

Insufficient data

Not yet reviewed

Copper

mg

5

1 (10T)

10

5

Fluoride

mg

Outside terms of reference

10

Not yet reviewed

Iodine

µg

500

500 (G) (940T)

1100

600

Iron

mg

15

17 (G)

45

Not yet reviewed

Manganese

mg

15

4 (G) (9–12T)

11

No recommendation,
insufficient data

Molybdenum

µg

200

insufficient data

2000

600

Nickel

µg

Not reviewed

Level not set (260T)

1000

Not yet reviewed

Potassium

mg

Not reviewed

3700 (G)

Not reviewed

Not yet reviewed

Selenium

µg

200

350 (450T)

400

300

Silicon

mg

Not reviewed

700 (760T)

Insufficient data
No recommendation

Not yet reviewed

Tin

mg

Not reviewed

13 (G, T)

Not reviewed

Not yet reviewed

Vanadium

µg

Not reviewed

insufficient data††

1800

Not yet reviewed

Zinc

mg

15

25 (42T)

40

25

G = Guidance level; T = Total intake;

*All amounts relate to 60 kg bodyweight adult and figures in parentheses are total (T) amounts from all dietary sources.  **d-α-tocopherol equivalents/day***Picolinates are excluded.


†Health Food Manufacturers’ Association, HFMA, December 1997. Germanium is not considered an essential element and was voluntarily withdrawn from use in UK.  ††The available studies are inadequate to support safe use of vanadium.  †††Implied in the text of the report