I’ve previously written a comment on the Holford Watch blog relating to the setting of RDAs in relation to the Orthomolecular Medicine claim that it is a myth that no-one is deficient in essential nutrients. Obviously, the OrthoMed rebuttal is of a straw man argument that “no-one” is deficient – which is not an argument I have ever heard used by any authority on nutrition – but I’m not here to talk about the use of logical fallacies by nutrition industry apologists. I’m here to tell you the truth about nutritionism, vitamins, recommended daily allowances and deficiency. The OrthoMed site claims that 50-60 per cent of Americans (up to 75 or 80% for some nutrients) are failing to achieve the RDA for certain vits and mins. That they are not achieving the RDA does not mean that they have a problem with vitamin deficiency. Ingesting less than the RDA for a vitamin does not mean that you will have symptoms of deficiency for the very good reason that:
“The term [RDA] recognises that particular groups of individuals (E.g. infants and those over 60) have different needs and for each group, the intention was to be sufficiently generous to encompass the presumed (but unmeasured) variability in requirement among people. This meant that the value was usually set deliberately high” [Derek Shrimpton]
Those setting RDAs have recognised that we are all individuals, with nutrient requirements that vary. They set the RDAs deliberately high in order to compensate for this variation in the amounts of nutrients require. Given that RDAs are usually set deliberately high it’s actually more likely that they are over and above our needs rather than being ‘sub-optimum’. But that won’t be enough to reassure some people – they will still worry about the low levels of vitamins they assume they are consuming. Or, perhaps, they may be worried about the perceived low intake of vitamins and minerals they are burdening their children with due to their failure to buy supplements. Here’s some reassurance for parents: the average child gets the recommended level of most vitamins and minerals. Don’t believe me? It’s been reported that: “the National Diet and Nutrition Survey found that the average child consumed levels of vitamins and most minerals that met recommendations, and in many cases, comfortably exceeded them. These conclusions were based on records from 7-day weighed food diaries and were confirmed by biochemical measurements of blood samples” [I think this is the study: doi: 10.1017/S0007114508981484, and here's a linky]
This story was linked to on the Bad Science miniblog, under the heading “Here’s something you won’t read in the papers”. To them, it would only be a story if the survey had shocking findings about the terrible state of our children’s health and all the horrible deficiency diseases they were at risk from. Good news like this does not sell papers. Or vitamin pills, come to that.
Edit 15th June 2009:
I really should have added some specific examples of when supplementation may be useful. Of course there is the specific advice that Folic Acid is recommended from the time you stop using contraception until the 12th week of pregnancy. There are also issues regarding Vitamin B12 status. One study found that of, 1424 pregnant women in Newfoundland during their first prenatal visit, “Serum vitamin B12 levels of 621 (43.6%) women were classified as deficient or marginal”. The need for women planning to conceive to increase their intake of Folic Acid has been addressed by the dissemination of advice to supplement 400 micrograms per day. That many pregnancies are unplanned means that there may be a much larger number of women who need to increase their folic acid/B12 intake than might otherwise appear.
Then there’s iron-deficiency anaemia: A Danish study (PMID: 8867722) found that “In general, Danish men and postmenopausal women had a satisfactory iron status. Adolescent Danish girls and premenopausal women had a high prevalence of iron deficiency, which should be taken into consideration when establishing guidelines and recommendations for nutritional iron intake in this section of the population”; a study in Bangladesh (European Journal of Clinical Nutrition (2001) 55, 598–604) found that “In all sub-groups, the intake of iron was much higher than the RDA level and mainly based on non-haem iron” and that “Prevalence of anaemia ranged from 63 to 70% in group L and 27 to 66% in group H, respectively”. I note that the iron intake was above the RDA and that it was mainly in the non-haem form. This may have implications for premenopausal women who are vegetarians or who exist on a restricted diet.
ETA: EVM report – vitmin2003