Aldosterone is the primary mineralocorticoid hormone in humans. The mineralocorticoids are those steroid hormones, secreted by the adrenal cortex that regulate the balance of water and electrolytes in the body. Working at the distal tubule and collecting ducts of the kidney, aldosterone increases the permeability of their inner membranes to sodium and potassium and is responsible for reabsorbing sodium (Na+) ions and water from the urine back into the blood, while secreting potassium (K+) ions into the urine. Aldosterone is responsible for the reabsorption of virtually all the sodium content in human blood under normal kidney filtration function. Aldosterone also acts on specific receptors in the brain to conserve water and salt by controlling renal tubular resorption.
Unfortunately, chronic high levels of aldosterone in the blood can have major negative consequences for the cardiovascular system, including to induce myocardial fibrosis, renal damage and stiffening of the arteries.
After its discovery more than 50 years ago, the medical interest in aldosterone has been dramatically renewed because of it’s immense impact on the cardiovascular system. Aldosterone is now considered to be the most important cardiovascular hormone in the human body.
As an integral part of the renin-angiotensin-aldosterone system (RAAS), a key function of aldosterone is to conserve salt (sodium chloride), when an insufficient amount is consumed. The latest research published in Clinical Endocrinology indicates that for most healthy humans, anything less than 6 g/day of salt (2300 mg sodium) will be insufficient to prevent the RAAS system from kicking in. That’s right – anything less than 6 grams of salt a day!
But the Dietary Reference Intakes recommends that an adequate intake of salt is 3.8 g/day of salt – not 6 g/day. In fact, the dietary reference intakes state that 6 g/day of salt is the tolerable upper limit of salt intake. How can one recommendation state one figure for a maximum intake while the scientific research indicates that very same figure is a minimum intake?
Perhaps the answer lies in the paper given at the Institute of Medicine workshop “The Development of DRIs 1994-2004: Lessons Learned and New Challenges” held in Washington September 18-20, 2007 by Dr. Peter Greenwald, Director of Cancer Prevention at the National Cancer Institute of the National Institutes of Health. Dr Greenwald described how most of the figures behind the recommended dietary intakes were based upon expert opinion (the lowest quality evidence) rather than randomized controlled double blind clinical trials (the highest level of evidence).
“Little research of the most useful type (randomized clinical trials) is available, whereas there is an enormous amount of information that is not very meaningful. This needs to be reversed.”
Later Dr. Greenwald goes on to say:
“To underscore the importance of “getting the science right,” we need only turn to a recent article in the New York Times Magazine written by a respected science reporter. It was entitled “Why can’t we trust much of what we hear about diet, health and behavior-related diseases?” (Taubes, 2007). The reporter includes several examples, many in nutrition epidemiology, where there is so much conflicting evidence that people do not believe it. Clearly, we have a serious problem, and we must push for the conduct of definitive studies before we make pronouncements on public health.”
As noted in an
earlier article, the latest evidence reported by Shapiro, Boaz et al from the Tel Aviv University Medical School reveals that healthy young adults who have been asked to limit their salt intake to 6 g/day (2300 mg sodium) were found to have elevated aldosterone levels indicating that their bodies were in a salt conservation mode. Unfortunately, these elevated levels of aldosterone quickly led to stiffening of the arteries. The conclusion was that for healthy young adults, the Dietary Guideline tolerable upper limit for salt was insufficient to prevent stimulation of aldosterone production. What would happen if the population actually consumed the level of salt recommended by the Guidelines? Would we be condemning an entire population to premature arterial stiffening? Would the government take responsibility for this or would it somehow contrive to blame the food industry for this problem?
In Europe, the EU Commission, led in large part by the UK and its Food Standards Agency has decided that public policy to reduce salt intake will trump basic human physiology. Charging forward pell-mell, the EU Commission, deliberately ignoring the latest scientific evidence, believes that they could not possibly go wrong on this issue because of the support of medical advocates, who have long ago given up any pretence of scientific objectivity.
The world has seen, time and again, that we ignore the science at our peril and as usual, consumers will end up being the victims.
The EU Commission has set the stage for the largest nutrition experiment ever carried out in history with the half billion citizens of the European Union expected to serve as the guinea pigs. When the compulsion to be seen as a driving force for change grabs policy makers by the throat, there is little left to do but allow that change to take place, regardless of the potentially disastrous consequences.
Not wanting to be perceived as being left out of this salt-reduction policy wave, Canada is set to follow suit – again totally ignoring the science and putting Canadian citizens at an elevated risk. One would think that some caution would be in order, but once again, backed by medical advisors and institutions that have done far more advocacy than homework, the government believes it cannot lose on this issue. Since when does ignoring the science and putting a population at an elevated risk give the Government a free pass?
So here we are, in the early part of 2008, with the drumbeat of scientific evidence piling up that the dietary guideline recommendations for sodium are largely irrelevant for the general population and insufficient to prevent production of elevated levels of aldosterone. For the majority of the people, salt, like water is a self-limiting nutrient. We know that aldosterone, chronically maintained at elevated levels as a result of reduced salt intake, will have major negative consequences on the integrity of our cardiovascular system. Like the mythical lemmings that march inexorably over the cliffs to their watery demise, it appears that the EU and Canada are on a track guided by what they don’t know, rather than by what they know – by urban myth and prejudice rather than science.
It is hoped that the new Committee selected to establish the Dietary Guidelines for 2010 will not feel obliged to make poor quality, knee-jerk decisions based upon subjective opinion and search out the most current scientific data upon which to establish their recommendations. Our health is at stake here.