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MAJOR MINERALS AND WATER

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In the 1960s, Lewis Dahl, a physician at the Brookhaven National Laboratory on Long Island, New York, spent a lot of time with rats. He was trying to understand the link between sodium and blood pressure, having noticed from national statistics that populations that eat low-salt diets, such as Eskimos, have a lower prevalence of high blood pressure than do populations that eat high-salt diets, such as the Japanese. To further explore this relationship, Dahl fed rats in his lab chronically high-sodium diets and observed them over time. He found that three-quarters of them developed high blood pressure (hypertension). He fed other rats low-sodium diets, and they rarely developed high blood pressure. As Dahl put it in a 1961 paper, “the evidence is unequivocal that, as the amount of salt ingested daily is increased, both incidence and severity of hypertension will be increased.” But then Dahl discovered something else interesting: When he fed his rats extra potassium along with the extra sodium, their blood pressure did not rise nearly as much as it did when he fed them sodium alone. In other words, sodium and potassium seemed to work against each other when it came to determining blood pressure—potassium protected against hypertension, while sodium increased the risk.

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We often hear that we should eat less sodium, but we don’t often hear that we need more potassium. Yet as it turns out, only 3% of American adults have usual intakes of potassium that exceed the Adequate Intake (AI) levels set by the Institute of Medicine. Indeed, so many of us do not get enough of the mineral that in 2010, the Dietary Guidelines for Americans identified potassium as a “nutrient of public concern.” Add to this the fact that we’re all eating way too much sodium—on average, we ingest 50% more than the government-recommended amounts—it’s no wonder that one in every three Americans has hypertension. According to a 2011 study published by researchers at the U.S. Centers for Disease Control and Prevention, a high consumption of sodium and low consumption of potassium work in concert to threaten health, increasing the risk of death from any cause by 50% and doubling the risk of death from heart attacks.

Sodium and potassium are two of the 16 minerals that are essential for human health and nutrition. Minerals are solid, stable inorganic elements. Unlike vitamins, minerals can’t be broken down into smaller constituents or destroyed by heat, light, cooking, or digestion. As the examples of sodium and potassium illustrate, both underconsumption and overconsumption of minerals can have a huge impact on human health and can have a range of physiological effects. Minerals have a variety of important jobs in the body, such as maintaining proper fluid balance and bone growth and maintenance.

Water is also an essential nutrient for the human body and it maintains health in multiple ways. Of the six categories of nutrients—the others being carbohydrates, lipids, proteins, vitamins, and minerals—water is arguably the most critical and indispensable. Because water is central to all our body functions, we can survive only a few days without it, while we can survive weeks without food. The primary ingredient in our bodies, after all, is water. The first part of this chapter is devoted to the topic of the major minerals. The second part discusses the role of water in health.