Nutrition & bone health
Potassium, the hidden bone guardian
by Dr. Susan E. Brown, PhD
Potassium is a mineral of great importance to the body — in fact, the adult Adequate Intake (AI) for potassium at 4,700 mg is nearly four times that of calcium (at 1,200 mg). While it is widely known that potassium, along with sodium, serves to maintain critical fluid balance within the body, its role in bone health is less well appreciated.
As it happens, the body has its own system of priorities for ensuring survival. Maintaining proper fluid balance inside and outside of the cells is a high priority indeed. The maintenance of systemic acid-base (pH) homeostasis is also held in very high priority, as alterations in blood pH balance can result in death within minutes. As the body produces various acids through its metabolic processes, there is a need to neutralize or buffer these acids with alkaline (base) compounds. To ensure acid-base balance, the body maintains diet-derived alkaline reserves in the blood, other fluids, and tissues. In addition, bone stores extra back-up alkaline reserves available for transfer into the blood when alkaline compounds in the blood, other fluids, and tissues run short.
Bone (and the hydration layer around bone) provides the only substantial extra reservoir of base available to titrate excess metabolic acids. When we exhaust all other available alkaline reserves, alkalizing compounds are drawn from in and around bone. This drain of alkalizing compounds from bone leads in turn to enhanced bone breakdown and loss of both bone mineral and bone matrix.
The role of potassium in bone health relates to the ability of selected potassium salts to neutralize bone-depleting metabolic acids. As discussed in my article on metabolic acidosis, these acids “eat away” at bone, much like acid rain eats away at a limestone statue. It is, however, is largely neutralized by potassium compounds, and to a lesser degree magnesium compounds, obtained from fruits and vegetables.
Fruits, vegetables, seeds, and most spices contain high amounts of potassium compounds. These potassium compounds (known as potassium salts) include alkalizing forms of potassium, including potassium citrate, potassium malate, and potassium gluconate. Within the body, these potassium salts are metabolized to yield potassium bicarbonate, which in turn provides the body with bicarbonate for neutralizing metabolic acids. If these mineral salts are not consumed in adequate amounts, alkalizing bone mineral compounds are drawn upon to help reduce low-grade metabolic acidosis, causing increased bone resorption and enhanced loss of minerals in the urine.
A variety of population-based studies now document the positive association between high intake of base-forming potassium and magnesium foodstuffs and bone health. For example, several studies with adults have found a positive association between fruit and vegetable intake and bone mineral density. In addition, urinary potassium, as a marker of potassium intake, is positively associated with bone mineral density in children. Overall, a beneficial effect on bone mass from high potassium fruit and vegetable intake has been shown in premenopausal and postmenopausal women, in the elderly, in children, and in men.
By neutralizing metabolic acids, potassium conserves calcium within the body and reduces urinary calcium loss. Potassium bicarbonate supplements equivalent to that found in 7-8 servings of fruits and vegetables were found to reverse the urinary calcium loss induced by high salt intake. Along the same lines, the DASH Intervention Trial found that simply increasing fruits and vegetables from 3.6 to 9.5 servings a day decreased urinary calcium loss from 157 mg per day to 110 mg per day. Looking at it another way, bone health expert Dr. Robert Heaney explains that eating one medium baked potato or one large banana can conserve about 60 mg of calcium within the body. To put this into perspective, a urinary loss of an extra 60 mg calcium per day would result in an 18 to 21% loss of total skeletal calcium over a decade.
Further, Dr. Sebastian and colleagues at the University of California were able not only to decrease urine calcium and phosphorus loss, but also able to decrease bone breakdown, and stimulate new bone formation in postmenopausal women by adding enough alkalizing potassium salts to neutralize metabolic acids.
Fruits and vegetables provide mineral salts with alkalizing compounds (as potassium citrate) useful for neutralizing net endogenous acid. In addition to promoting an alkaline environment, a diet high in fruits, vegetables, and legumes provides nutrients such vitamins C, E, A, and the B’s, quercitin, and many other phytochemicals that also promote bone health. Increasing vegetable and fruit intake is the preferred way to increase potassium intake and carries multiple benefits for blood pressure normalization, stroke risk reduction, and weight control, in addition to being bone-protective.
The current U.S. “Adequate Intake” recommendation for potassium is 4,700 mg/day, (the equivalent of about 13 half cup servings of fruits and vegetables a day). The average adult daily potassium intake in the U.S. is much below the AI and is reported to average around 2,200 mg for women and 3,200 mg for men.
Unquestionably, potassium is one of the most important key bone nutrients, and consuming the recommended amount of 4,700 mg potassium a day should be a top priority for everyone. (For a list of wholesome food sources of potassium, see our potassium nutrition chart.)
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Original Publication Date: 01/01/2009
Last Modified: 07/10/2012
Principal Author: Dr. Susan E. Brown, PhD