How much vitamin or mineral your body need?
Q. How do I determine how much of a vitamin or mineral I need?
A. Most nutrition experts recommend you start with the RNI’ or RDA (recommended daily allowance.)
Q. I have heard of RNI but what are they precisely?
A. An RNI is defined as amount of intake nutrients, which on the basis of current scientific knowledge is believed to be enough to meet the known nutrients needs of almost all healthy people. This seemingly circular definition means that an RNI states how much we are believed to need each day to present us from suffering the ill effects which result from not taking enough. Complying with all the RNI will not necessarily keep us healthy but it should keep us from developing vitamin and mineral deficiency diseases.
Q. Are the RNi the same for all ages and for sexes?
A. No. Different RNI are set for people of different age and sexes. If you look at a typical RNI chart such as that produced by the British Department of health you will find the recommended daily amounts of such things as energy, protein, calcium, iron, vitamin A, thiamine, riboflavin, niacin, vitamin C and vitamin D for boys and girls separately at various ages from under 1 year and 17 years, for men 18 – 34 years of sedentary moderately active and very active habit, for men aged 35-64 in the same three groups for men aged 65-74 years for men 75 and over; for women, 18-54 in most occupations and for those who are very active for women 55-74 ;foe women 74 and above for pregnant women and for women who are breastfeeding. This official table makes no recommendations for any of the other nutrients because the Ministry experts believe that the requirements for these are more than if a good mixed diet is taken.
Q. How are RNI determined?
A. Every few years various committees official and other wise review the scientific literature on a particular nutrient and come up with new recommendation, as a result RNI are never engraved on stone and comparison of RNI over the years make interesting reading. These committees looked ate a number of diets containing low or deficient levels of nutrient followed by correction of the deficit with measured studies that measure blood or tissue levels of a nutrient in relation to intake studies related to amounts so high that they cause harmful side effects and so on.
Q. Sounds like they have good solid information on which to base their recommendations. Is that the case?
A. Unfortunately, no. that would be ideal but in reality a lot of information is lacking. This makes the RNI less reliable and accurate than they might be.
Q. What kind of information is lacking?
A. Well for a start we don’t have enough information on the nutritional requirements of women and children. Most nutrition studies have used young men as subjects yet the results are often applied to women of all ages, children and older men. Some of this committee take into account the results of dietary surveys questionnaires which ask people what that eat. Unfortunately dietary surveys are notoriously inaccurate. People simply don’t know, don’t remember or don’t want to remember what it is they eat. So even the best dietary survey methods are unreliable.
Q. You haven’t mentioned anything about the RNIs and the analysis of an individual’s diet? Why is that?
A. RNI were not designed to be used to analyze an individual person’s diet. However they are often used for exactly this purpose because they are the only available sources of information on the matter.
Dietitians take the view that the majority of people under normal conditions doesn’t need more than the RNI of a nutrient for a normal functioning, In fact it is not until someone’s intake drops70 per cent of the RNI that it is usually considered on the low side.
Q. In that case, why don’t the authorities simply lower the RNI?
A. In fact, this does sometimes happen. Quite a number of nutrients have had their RNI cut back
Q. Which RNI have been lowered?
A. Protein has gone down several times. Fats folic acid B12, thiamine, riboflavin and niacin have all been lowered in some categories. And for women recommendations have been lowered for zinc and iron.
Q. Why were the RNI lowered?
A. To reflect increasing knowledge and also of changing opinions as to value of various nutrients.
Q. This sounds strange to me, since I have read that higher amounts of some nutrients can provide important benefits. Am I wrong?
A. No. it seems strange to lot of nutrition researchers too. In fact the reduced RNI have churned up a major controversy today in nutrition the question of adequate nutrition versus optimum nutrition.
Some nutrition experts agree that most people in the developed world, but certainly not all are adequately nourished. That is they do suffer from the vitamin deficiency disease described earlier such as rickets, scurvy, or beriberi even mildest forms. On the other hands new research appears to show that many people do not get optimal amounts of some nutrients amounts that not only prevent deficiency diseases but also help to recently been linked with vitamin or mineral intake. These diseases include the serious arterial diseases atherosclerosis which causes heart attacks and strokes cancer and diabetes some doctors contend that the list should include most illnesses.
This new research is causing doctors to re examine and often abandon old theories and definitions. Today many people are aiming not just to avoid deficiency disease but to promote long life and optimum health.
Q. Do you have any examples of adequate versus optimum amounts?
A. lets take vitamin E for example. The RNI for this vitamin 15 IU but research suggests additional benefits at much higher amounts 300 IU or more. Many major research projects are showing that the antioxidants effect of this vitamin and vitamin C in combating damaging free radicals cal lower the incidence of a wide range of free diseases and perhaps even shoe the effects of aging.
Q. Are the RNI ever going to take this new research into consideration?
A. In due course very likely. But there is no official word on that yet.
Q. So where does that leave me now? Am I supposed to use current RNI to decide what to eat?
A. For the time being you will have to consider them you best available source of information. You may also want to check the amounts recommended by researchers doing work on a particular nutrient.
Q. In there anything else I need to know about the RNI?
A. Yes. Although they are calculated for people with some special needs such as pregnant women and nursing mothers they do not cater for the needs of people who are sick or who have trouble absorbing nutrients from their intestines as would someone with crohn’s or celiac diseases for instance. Furthermore the RNi also may not adequately address the needs of older people.
On the other hand current RNI do go beyond the absolute minimum for preventing deficiency related diseases. They have a built in margin of safety.