A 10-year follow-up study, involving 2642 adults (age range, 71-80 years) has recently been published, and has concluded that there is no link between salt intake and risk of cardiovascular disease. The results were split into 3 groups, and are as follows:
- Those who consumed less than 1500mg sodium (3.75g salt)/ day had a 33.8% risk of cardiovascular disease.
- Those who consumed between 1500mg to 2300mg sodium (3.75g- 5.75g salt)/day had a 30.7% risk of cardiovascular disease.
- Those who consumed more than 2300mg sodium (5.75g salt)/day had a 35.2% risk of cardiovascular disease1
These results show that all groups had a similar risk of developing cardiovascular disease, regardless of salt intake. In fact, 3.75g – 5.75g of salt a day seems to be slightly healthier than the other categories, but its not statistically significant. So, in a world where we are constantly told to always try and reduce our salt intake, what do these findings mean? Is there no relationship between salt intake and cardiovascular disease/ heart failure?
A close look at the study
The study is a good one – it has a large population, which will minimise the effect on anomalies and it covers 10 years, so has a pretty good data range. It’s certainly not a small pilot study, and the results are significant. However, as with almost all studies, there are short comings, the most obvious being the use of the infamous food frequency questionnaire (FFQ), which is notoriously inaccurate. People always report what makes them look good, not what is accurate, and so under report on consumption of bad things (sugars, salts, etc). I’ve seen obese peoples FFQs which report that they have only eaten 1000kcals a day. Sure, kcals aren’t everything, but it takes much more than 1000kcals to make you over 40% body fat…
So what this means in terms of this study is that the participants are quite likely to have under reported their salt intake. This is just the nature of this kind of study, and aside from keeping all participants in controlled conditions for 10 years, there is nothing you can do about it. The degree of under reporting is difficult to determine, but the benefit of the large population is that any extreme under reporting will have very little effect on the actual results. Still, it is likely that the salt intake in each group was more than reported, and this actually strengthens the argument that salt has no meaningful impact on cardiovascular disease.
Relevance/ value of data
The UK National Health Service recommends 2400mg sodium (6g salt)/ day for each adults2, and this value is reflected in the 3rd test group who were consuming more than 2400mg sodium (5.75g) salt each day. Considering that people will have under reported their salt intake, we can assume that these people would have been consuming at least the RDA of salt on a daily basis, and probably more. Group 3 could have been consuming just over the RDA though, we don’t know. I would personally liked to have seen a 4th group, where the minimum salt consumption was around 8g (3200mg sodium), which is the average daily consumption of salt in the UK 2.What this study does show is that perhaps the RDA could be more than 6g of salt – not terribly valuable.
Not being a terribly conclusive study, I decided to research how much salt really is healthy…
Further research on salt
Salt & cardiovascular disease
An article published in the Pan American Journal of Public Health in 2012 clearly states that salt intake of 8g and upwards causes raised blood pressure, and even goes as far as to recommend salt intake should be no more than 3-4g3. These findings are in keeping with a report published in the British Medical Journal, which combined the results of at a number of studies totalling 177,025 participants. Some of these studies were up to 20 years long, and the report concludes that ‘high salt intake is associated with significantly increased risk of stroke and total cardiovascular disease’. There is also a Cochrane review (which many people accept as the gold standard in unbias and thorough research) on how much salt is healthy. This review included 34 randomised trials, and concluded that a modest reduction in salt over 4 weeks or more causes a significant reduction in blood pressure, and so a reduction in risk of cardiovascular disease. The review even went as far as saying that salt consumption should be reduced to as little as 3g/day for greater benefits4. There are many studies which follow this same theme (both big and small), it just takes a quick search on Scientific Journal databases to find them so I won’t include them all.
There certainly is a lot of evidence to suggest that salt consumption should be dramatically lowered, but how low?
Benefits of salt
The Journal of the American Medical Association (JAMA) reported that salt consumption less than 3g/ day increases the risk of cardiovascular death and hospitalisation for congestive heart failure, but consumption more than 7g/ day was associated with an increased risk of all cardiovascular events5. This study doesn’t advocate large salt consumption, but does contradict the finding of some studies, which seem suggest that the least salt possible is the best.
There is also evidence that sodium loading before exercise helps retain water in hot weather6, which is great for those interested in cycling log distances, but the study doesn’t mention anything about long term effects of salt. Furthermore, the study only includes 8 people – hardly a strong argument for consuming large amounts of sodium in light of other evidence.
One common argument for the consumption of salt being healthy is that the Kuna (a tribe native to Panama who have very low salt consumption and low hypertension) show no signs of developing hypertension when their salt intake reaches 2.6g-6g/day7. It is interesting that dramatic salt increases has little impact on the health of the Kuna, but it offers us very little insight onto the impact of salt on the Western world. The Kuna, like most tribes, have quite an isolated gene pool which differs greatly to you and me; meaning their results are unlikely to translate over to us. Also 2.6g is not going to show signs of hypertension in modern society, and in reality nor is 6g. Results from this study aren’t particularly relevant, nor do they show much insight into the effects of salt on our health.
There is also evidence that salt consumption can help metabolise the dreaded stress hormone cortisol – something which many people in the modern world can benefit from. This is a clear benefit of salt consumption, but how does it impact on cardiovascular health? Is it a worthwhile pay-off to help cortisol metabolism, but increase blood pressure? Not in my eyes.
So, how much salt is healthy?
Despite a variety of studies all being conducted in different ways and using different measurements for ‘health’, there is some consistent and useful information which can be extracted:
- Dosages lower than 3g can increase the risk of cardiovascular death.
- Dosages of 7g+ do increase the risk of high blood pressure and cardiovascular disease.
- Short term high dosages will have no significant effect on blood pressure, but can help metabolise cortisol and improve water retention (when doing exercise in hot weather at least). This makes salt consumption before sports beneficial.
- The healthiest group in all studies consumed the RDA of salt 4-6g/day.
The bottom line
Salt is tasty – and adds flavour to meals. We as humans enjoy the flavour salt for the same reason we enjoy the taste sweet things– they were both extremely beneficial for our survival during our evolution and so we developed a strong desire for their flavour. So much so that we have refined and extracted them into a cheap, pure and unhealthy forms.
If you want to consume a healthy amount of salt stick to the number 1 rule of keeping healthy, and only eat unprocessed foods, because the salt content of them is much lower than highly processed foods. If you want to add salt to your meals, thats fine (within reason), but again, stick to the number 1 rule, and ask yourself where can you get salt in a natural form. Sea salt is a much healthier than table salt for example. It is simply evaporated sea salt water, and not only contains sodium and chlorine (the minerals which make up salt), but also contains magnesium, potassium and other minerals which are essential for health.
So don’t stop using salt. Rather stop eating highly processed foods regularly, and start using sea salt to flavour your meals. This way your salt consumption will naturally be at the healthy level.
1. JAMA Intern Med. Published online January 19, 2015. doi:10.1001/jamainternmed.2014.6278
2. NHS. (2013). How much salt is good for me? . Available: http://www.nhs.uk/chq/pages/1138.aspx?CategoryID=51. Last accessed 04/02/2015.
3. He FJ. (2012). Reducing salt intake to prevent hypertension and cardiovascular disease.. Rev Panam Salud Publica. 32 (4), 293-300.
4. doi: http://dx.doi.org/10.1136/bmj.f1325 (Published 04 April 2013).
5.National University of Ireland. (2011). Study calls sodium intake guidelines into question. Available: http://www.sciencedaily.com/releases/2011/11/111123132935.htm. Last accessed 04/02/2015.
6. Sims ST. (2007). Sodium loading aids fluid balance and reduces physiological strain of trained men exercising in the heat. Med Sci Sports Exerc. 39 (1), 123-30.
7. Norman K. Hollenberg. (1997). Aging, Acculturation, Salt Intake, and Hypertension in the Kuna of Panama. Hypertension. 29 (1), 171-176.
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