Chloride is an electrolyte which alongside calcium, sodium and potassium helps to regulate fluid and electrical signals in the body.  Changes in chloride levels nearly always change with sodium levels.
Chloride helps to keep the acid-base balance of the body in equilibrium. It also has a vital role in sodium to keep the water in the body at normal levels.
Chloride is found predominantly outside our cells and regulates the water going in and out of the cells. Chloride in conjunction with sodium also helps to regulate our blood pressure and blood volume. Increases in chloride can cause our blood pressure to rise and increase fluid retention. However, we can lose chloride when we lose fluid from our body e.g. sweating after exercise or on a hot day, blood loss can also cause a loss of chloride.
High levels of chloride in the blood can be a sign of dehydration. Dehydration can cause several symptoms including confusion. You may also experience low energy levels. High levels can occur with high sodium levels in the blood. This could also be an indication of kidney disease. It occurs when too much base is lost from the body or through hyperventilation.
Low chloride levels occur with low sodium levels. It may also occur at the same time as other medical conditions such as heart failure, lung disease or following a prolonged bout of vomiting.
Intense exercise can lead to a decrease in chloride levels and so it is important to replenish the electrolytes you lose.
Keeping your chloride levels within a normal range should be able to be achieved by eating a balanced diet and ensuring you are hydrated throughout the day. Chloride is present in most natural foods such as meat and vegetables. It is more abundant in table salt, olives, tomatoes, celery and lettuce.
Exercise is an important aspect of a healthy lifestyle. However, it is important to remember that intense exercise can make you sweat excessively. Sweating is one way in which the body can lose electrolytes including chloride. Therefore, you should keep yourself hydrated either with water and/or isotonic drinks.
 Fong, P and Gray, M, A. (2006). Orchestration of Vectorial Chloride Transport by Epithelia. In: Bittar, E, E and Pusch, M ed. Advances in Molecular and Cell Biology.