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"Canada’s leading health experts are finally sounding the alarm: Excessive sodium is poisoning our population and creating an entirely preventable public-health crisis," writes Carly Weeks in Saturday's Globe and Mail.

"About five million Canadians have high blood pressure, and Norm Campbell, a medical professor at the University of Calgary, says that simply cutting dietary sodium would eliminate one case out of every five. 'I think it really is a time for action,' says Dr. Campbell, who was appointed the first Canadian Chair in Hypertension Prevention and Control by the Canadian Institutes of Health Research and a coalition of other groups in 2006. 'It’s almost negligent we haven’t done something about this before.'"

Dr. Campbell was online earlier to take your questions about our government's policy around the way food manufacturers treat salt, as well as its effect on our health.

Dr. Campbell is a professor of medicine at the University of Calgary. Dr Campbell holds the CIHR Canadian chair in hypertension prevention and control and is the chair of the Canadian Hypertension Education Program (CHEP) steering committee and the CHEP executive committee. CHEP develops, implements and evaluates the impact of Canadian hypertension recommendations. Dr Campbell is also the president of Blood Pressure Canada, a coalition of 25 organizations dedicated to the prevention and control of hypertension in Canada.

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Margaret writes: It is my understanding that, unless specifically requested, none of the industrial salt used in Canada is iodized. Even the little packets of salt at the restaurants are not iodized. That leaves us consuming way too much sodium and almost no iodine. This is a public health travesty right up there with industrial milk products almost never being fortified with vitamin D. Fortunately a few brands of yogurt are now getting past this issue. The question is: Are we seeing the results of iodine deficiency in Canada as a result of this practice?

Dr. Campbell: In Canada, the salt used by food processors usually does not contain iodine, while the salt we buy in food stores for use in cooking and at the table is usually iodized. Iodine deficiency is rare in Canada according to experts at Health Canada and I have very, very rarely heard of anyone in Canada with iodine deficiency in my clinical career of 25 years. However, in many developing countries, iodine deficiency remains an important public health issue. In these settings increasing the amount of iodine added to salt, adding iodine to salt used in food processing and adding iodine to other food sources are potential solutions to preventing iodine deficiency while lowering dietary sodium.

Disease associated with high sodium intake is very common both in Canada and in developing countries.

Duke writes: Hi Dr. Campbell: I eat little or no salt. I have a little on my soft boiled egg in the morning and I may put a few drops of soy sauce on my fish in the evening. My blood pressure is low, and in the morning too low. 110/55 . Once I am up and about may go up to 115/70, which is good for my age (79). That's the good part. Now, my problem is that when I hike or exercise I get hot and drink water. But I do get dehydrated, despite the water. I may feel dizzy or sleepy if I lose too much sweat. I have been told that I get dehydrated because I don't take enough salt. It was suggested that I eat salted crackers, while exercising or hiking. What do you think? How much salt does a person need when doing physical work and how much when not? I don't want to over-do it.

Dr. Campbell: Many Canadians believe they eat little salt if they add little in cooking or at the table. However most of the sodium is added during processing of food so that on average Canadians are eating more than twice the amount recommended as adequate and the majority are eating more that the upper limited recommended for health. It is very difficult for Canadians to eat a healthy amount of salt because it is ‘hidden’ in processed foods that are often not labeled or the labels are difficult to understand. A Health Canada Work group is developing plans that include working with food processors to reduce the amount of salt added to food and many food processors have made commitments to reduce the amount of salt they are adding to food. Canadians should look for foods with less salt in them.

Low blood pressure, if it is not caused by a disease such as a heart attack or heart failure, is generally a sign of good health. Lower blood pressures help prevent damage to blood vessels that occur with aging. Blood pressure related damage occurs even at blood pressure that are considered normal and the World Health Organization has indicated that blood pressure above 115 mmHg (systolic or the top number) is the leading risk for death in the world.

Some people who are not used to hot temperatures or hard physical activity do require more salt for a few days. A sign that you require more salt and water is a feeling of being dizzy. Having a small amount of extra salt by eating a salted food can help in this situation but mainly ensure that you are drinking enough water. The exact amount depend on how much work you are doing and how hot it is. In people such as our Olympic athletes who are used to hot weather or heavy physical activity no extra salt in the diet is required.

Deanna writes: Hi Dr. Campbell, What are the risks of sodium for someone without high blood pressure? I am a 37 y.o. female. I have (and always have had) low blood pressure. Recently doctors (family doc and endocrinologist) have been telling me to 'salt load'. I am to eat 3 Bovril cubes a day - and add lots of salt to all my foods. The Heart and Stroke info. makes it sound like salt is a toxin, and everyone (even toddlers) should reduce their sodium. What are the immediate and long term negative effects of sodium for those of us without high blood pressure - here I am thinking toddlers, low blood pressure people and normal blood pressure people?

Dr. Campbell writes: The main risk of high dietary sodium is increased blood pressure and it occurs over a long period of time. As you get older your body is less able to get rid of the sodium you eat and the sodium is more likely to increase your blood pressure. It is estimated that 9 in 10 Canadians will develop high blood pressure as they get older even if their blood pressure is normal at age 55. It is estimated that about 3 in 10 Canadians have hypertension because of the high amount of sodium in our diets. Even in children high sodium in the diet increases blood pressure and it is believed that this leads to hypertension when they become adults. Eating less sodium helps prevent hypertension. In animals that eat a large amount of sodium, there is some damage to their heart and blood vessels even if the blood pressure is not increased. There are a few rare diseases that are treated by increasing the amount of sodium in the diet. You will need to talk to your doctors to find out if this is your situation.

In the long term there are other health issues associated with high dietary sodium, but there has not been enough research done to know that the sodium is the cause of the problem. Diets high in sodium are associated with stomach cancer. In animals that eat cancer causing substances, stomach cancers form more often in the animals that also eat high amounts of sodium. Stomach cancers also occur more often in people who live in areas where there is more sodium in the diet.

Other health issues associated with high dietary sodium include osteoporosis and calcium kidney stones. When people eat high amounts of sodium this washes calcium out of body through the kidneys. The lost of calcium from the body is thought to cause osteoporosis and the increased calcium in the urine is thought to be a cause of kidney stones. High dietary sodium is also believed to make asthma worse. Also when you eat more sodium you become more thirsty. In some studies, obesity in children has been linked to high sodium diets because the children who eat more sodium drink more pop and other drinks that are high in calories. Unfortunately there has not been enough research to know with certainty if sodium causes these important health issues that are very common in Canada.

It is important that sodium is only one issue with diets and government, industry and health groups are working together to make Canadians healthier by reducing the amount of sodium in our diets. However, a healthy diet is much more than a low salt diet. Most Canadians need to eat more fresh fruits and vegetables, and less saturated and trans fats, sugars and red meat. Canada’s guide to healthy eating provides information on a balanced healthy diet. Many if not most of the diseases that currently affect Canadians are caused at least in part by our poor dietary habits.

Blane writes: I'm curious where the 1500mg number for daily recommended sodium intake comes from in the Globe's articles. Reading the 'Nutrition Facts' on the back of my Kraft Dinner box I find that a serving has 350mg of sodium which it then says is 15% of my daily recommended value. This number suggests that my daily recommended value of sodium would be 2333mg (i.e. 350/0.15) rather than 1500mg. Looking at the back of my fruitsnacks package I find that a serving is 55mg of sodium which it then says is 2% of my daily recommended value. This number suggests a daily recommended value of 2750mg (i.e. 55/0.02). So where does the number 1500mg come from and if this is the number I should be aiming for then what is the information in the Nutrition Fact box telling me? Am I misinformed by the numbers given in the Nutrition Fact boxes?

Dr. Campbell: The Institute of Medicine was commissioned by the Canadian and American governments to develop daily recommended intakes for Canadian and American diets. A daily sodium intake of 1500mg is recommended as adequate for those aged 9 to 50 by the Institute of Medicine. The recommended intakes vary depending on age and lower levels are recommended for those less than age 9 or over age 50. Less than 2300mg sodium/day is the upper limit for health recommended by the Institute of Medicine for most age groups, with lower levels recommended for those under age 14.

On a historical basis, Canada and the United States has used 2400mg as a basis for calculating the percent daily value. This is clearly a confusing situation. Many have suggested the percent daily value should be based on the adequate daily intake value (generally 1500mg), however the different levels of adequate intake level in different ages could make that suggestion complex and confusing as well. Further, some manufacturers adjust the proportion size on which the daily value is determined which could mislead people to believe there is a lower amount of sodium.

In Canada, it is hoped part of the process to reduce dietary sodium will involve clarifying and making the nutrition facts label easier to understand. Health Canada is reassessing labeling; hence this is opportune time to provide input. In the United Kingdom, a simple easy to understand and effective color coded nutrition 'wheel' has been used by some grocery chains to inform customers if the food is low, intermediate or high in sodium and other nutrients that are potentially harmful to health in excess.

Carolyn writes: I try to avoid salt as much as I can (no processed foods with salt, no added salt to food before or after cooking) but I understand that it's possible to have too little salt. I assume that the daily recommended amount is a maximum and not a minimum. What is the minimum amount necessary to maintain good health for a reasonably active healthy non-pregnant woman? What are the symptoms of too little salt?

Dr. Campbell: It is difficult with current knowledge to know how low sodium can be in the diet and be safe. The Institute of Medicine was unable to define a lower limit of sodium in the diet that was unsafe. It has been estimated that the diets of people living before industrialization contained approximately 700mg/day of sodium from natural food sources.

In those societies, individuals where highly physically active and many lived in warm climates. In individuals who suddenly become physically active, in particular in hot dry weather they may lose excessive sodium and require higher amounts for a short period in time. This process of adapting to the higher activity and heat occurs in less than one week and more sodium in the diet is not required long term. Some people with rare diseases do require a high sodium intake and these people need medical care and advice.

The recommended upper limit and adequate intake of sodium in the diet is for individuals in good health. No minimum amount of sodium has been established to maintain good health. In certain circumstances, such as, severe vomiting and diarrhea, extra salt and water can be lost and in these situations rehydration with salt and water is required. The symptoms are those of thirst and low blood pressure (feeling weak and dizzy or fainting). It is important that many of these symptoms have many causes that may not relate to low blood pressure or to a need for extra salt and water.