Reducing salt intake is said to have a beneficial effect on blood pressure, especially among those who already suffer from hypertension (high blood pressure), however, one of the undesirable effects of consuming much less salt is a higher risk of elevated levels of blood cholesterol and triglycerides, researchers from Denmark reported in The American Journal of Hypertension. They also found that the benefits of sodium reduction on blood pressure are tiny.
Salt, commonly referred to as table salt is a mineral mainly composed of sodium chloride - NaCl. Salt is vital for animal life. However, excess amounts are damaging for animals and plants. Saltiness (the taste of salt) is one of the basic human tastes. 39.3% of table salt's weight is made up of sodium. The upper limit for a typical adult in the UK is 4,000 for salt and 1,600 for sodium (about 39.3% of the total). In the USA it is 5,750 for salt and 2,300 for sodium (and lower upper limits for some special groups). Experts say it is the sodium in salt that appears to have an impact on blood pressure.
The authors explained that recent population studies have linked sodium consumption with illness and higher death rates (morbidity and mortality). These studies have triggered various moves to get people to reduce salt intake as a preventive measure (prophylaxis). However, they add that many of the studies have conflicting evidence.
The researchers added that recent studies have shown that reducing salt intake for a patient with diabetes or heart failure may actually be harmful.
So far, salt intake reduction recommendations have been based on its effect on just one marker - blood pressure. Believing that consuming less salt protects from heart disease and early death is still a "hypothetical benefit", the researchers explained.
Some other studies have shown that consuming less sodium may have some other benefits. This latest review is a second update - it is a study of several studies (meta-analysis) which also looks at salt's impact on hormones and lipids (fats), as well as blood pressure.
Dr. Niels Graudal, from Copenhagen University Hospital in Denmark, and team set out to review the impact of a low-dietary sodium intake versus high intake on:
- Systolic blood pressure (SBP) - the blood pressure when the heart contracts; the higher number
- Diastolic blood pressure (DBP) - the blood pressure between heartbeats; the lower number
- Mean blood pressure (BP)
- Blood (plasma) levels of:
- Aldosterone - a hormone secreted by the adrenal gland which regulates salt and water balance in the body
- Catecholamines - any of a group of amines that have vital physiological effects as neurotransmitters and hormones, such as epinephrine, norepinephrine, and dopamine
- High-density lipoprotein (HDL) - also known as the "good cholesterol"
- Low-density lipoprotein (LDL) - also known as the "bad cholesterol"
- Renin - hormone produced by special cells within the kidney
- Triglyceride - a major form of fat stored by the body
They reviewed 167 studies and found that reduced salt intake had a very slight benefit in lowering blood pressure, but that cholesterol and triglyceride levels rise. The average drop in systolic BP was -1.27 and diastolic BP was -0.5 - a negligible benefit.
However, lower sodium intake resulted in a considerable increase in plasma cholesterol (2.5%) and plasma triglyceride (7%) - a much larger increase than the drop in blood pressure. Levels of aldosterone, epinephrine, and norepinephrine also all went up. These rises are linked to a higher risk of kidney problems or blood vessel constriction.
The authors wrote that:
"Due to the relatively small effects and due to the antagonistic nature of the effects...these results do not support that sodium may have net beneficial effects in a population of Caucasians."
Caucasian patients with hypertension might benefit from lower sodium intake "as a supplementary treatment", they added.
Regarding possible benefits for Asians and African-Americans, the authors wrote:
"In Asians and blacks, the effect of sodium reduction was greater, but at present too few studies have been carried out to conclude different from that above."
Written by Christian Nordqvist