Islamabad - A controversial new study has suggested that eating too little salt can increase a person’s risk of heart disease, heart attack and stroke.

It has long been held that a diet high in salt is dangerous to the heart, raising the risk of heart attack and stroke. But, in a dramatic U-turn, the scientific evidence has suggested the opposite can also be true.

A global study has found that, contrary to past belief, low-salt diets may not be beneficial. Rather, they can increase the risk of cardiovascular disease and death, compared with average salt consumption.

The study has garnered strong reaction, with one expert declaring his ‘disbelief,’ while others are critical of the study’s methods, and calling its findings into question.

The research was carried out by investigators at McMaster University and Hamilton Health Sciences. They analyzed more than 130,000 people across 49 countries, focusing on whether the relationship between sodium (salt) intake and death, heart disease and stroke differs in people with high blood pressure compared to those with normal blood pressure.

Their findings showed that regardless of whether people have high blood pressure, low-salt intake is linked to a greater incidence of heart attacks, stroke, and deaths compared to average intake.

Dr Andrew Mente, lead author, and associate professor of clinical epidemiology and biostatistics at McMaster’s Michael G. DeGroote School of Medicine, hailed the findings ‘extremely important’ for those suffering high blood pressure.

He said: ‘While our data highlights the importance of reducing high salt intake in people with hypertension (high blood pressure), it does not support reducing salt intake to low levels.

‘Our findings are important because they show that lowering sodium is best targeted at those with hypertension who also consume high sodium diets.’

The NHS advises adults in the UK eat no more than 6g of salt each day - around one teaspoon.

The evidence supporting global actions for a moderate reduction in salt consumption to prevent cardiovascular disease is strong and such studies should not overturn the concerted public health action to reduce salt intake globally

Professor Francesco Cappuccio, of the WHO and University of Warwick 

In the US, the Centers for Disease Control and Prevention (CDC) recommends Americans consume less than 2,300 miligrams a day. That comes in the face of evidence, suggesting the average American consumes 3,400mg each day.

Meanwhile, in Canada, typical sodium intake is between 3.5 and 4g per day. However, some guidelines have suggested that the entire population lower their salt intake to below 2.3g a day - a level that fewer than five per cent of Canadians and people around the world consume.

In the past, some research has shown that low-salt diets, compared to average intake, is linked to increased cardiovascular risk and mortality, even though low sodium intake is linked to lower blood pressure. This new study shows that the risks linked with low-salt intake - classified as less than three grams a day - are consistent regardless of a patient’s blood pressure. 

Adolescent diet may impact later-life breast density, breast cancer risk

High breast density is known to be associated with an increased risk of breast cancer. New research demonstrates dietary factors in adolescence that might lead to higher-density breasts in adulthood. If the results are confirmed, the dietary habits of teenagers could potentially increase their chance of breast cancer decades later.

Adolescent diet may alter the density of breast tissue in adulthood.

Breast cancer is one of the most common cancers in women; 224,147 American women were diagnosed in 2012.

There are a number of known risk factors for breast cancer, including early onset periods, late menopause, and having the first child over the age of 30.

Studies show that dense breasts also increase the likelihood of breast cancer. The reasons for this link are not yet known.

Breast density refers to breasts that have a relatively high volume of fibrous or glandular tissue compared with fat. Contrary to popular belief, breast density cannot be judged by how a breast feels to the touch. In other words, if a breast is firm, this does not necessarily mean that it is dense.

Researchers Seungyoun Jung and Prof. Joanne Dorgan, from the Department of Epidemiology and Public Health at the University of Maryland School of Medicine, set out to investigate dietary factors that might influence the density of breast tissue.

The breasts are most sensitive to external factors during adolescence. This is a time when they are developing and undergoing structural change. As such, the team concentrated their focus on this pivotal stage of development into womanhood.

The researchers used data from the Dietary Intervention Study in Children (DISC). DISC was a clinical trial that started in 1988 and involved 301 girls aged 8-10 years. The study assessed the diets of these individuals across the following years.

During the DISC follow-up study, carried out when the participants were aged 25-29, the breast density of 177 women was measured using magnetic resonance imaging (MRI).

Before analyzing their results, Jung and Prof. Dorgan adjusted for an array of variables; these included number of live births, adult weight, race, education level, and total protein and energy intake.

Once these factors had been taken into account, the results showed that adolescents consuming higher quantities of saturated fat and a lower intake of mono- and polyunsaturated fats had an increased percentage of dense breast volume (DBV).

Women whose fat intake fell in the highest category had a mean DBV of 21.5 percent, whereas those in the lowest category had a mean DBV of 16.4 percent.

A similar, but opposite, effect was seen when the lowest and highest monounsaturated fat intake were compared; those consuming the least had the highest density breasts.

“[...] there is a gradient of increasing breast cancer risk with increasing breast density, the differences in percent DBV we observed across extreme quartiles in our study, if confirmed, could potentially be of interest with regards to later breast cancer risk.”