The population studies have shown that an improved potassium to sodium ratio from high potassium foods in the diet has resulted in fewer hip fractures. The improved ratio has even resulted in increased bone mineral density. For the improvement in bone strength to result from the improved ratio, and not just be associated with it, the basic science should support the result. Ideally a systems approach would show all the effects from the interactions of the important factors influencing bone strength. That is in the future. But at least the various basic science studies should be consistent with the importance of the ratio.
For osteoporosis this means the studies of osteoclasts, osteoblasts, osteocytes, bone matrix, hormones and environmental influences should be consistent with the importance of the potassium sodium ratio. The discussion today will be limited to studies of the osteoclast- the cells that dissolve bone matrix.
How Osteoclasts Remodel Bone
Osteoclasts are active during all bone remodeling, whether the bone is getting thicker or thinner. Their activity alternates between resorptive and motile phases. During the resorptive phase the osteoclast sits adjacent to the bone matrix, which is the acellular hard part of bone. It releases enzymes that breakdown proteins in the matrix, putting bone minerals into solution outside the cell. During the motile phase the cell moves from one location where it is sitting against the bone matrix to another location against the matrix.
This change in mineral ion concentration outside the cell during the resorptive phase leads to a change in the electrical charge of the cell's plasma membrane. The change in electrical charge of the membrane shifts the states of multiple pores and channels in the membrane between open and closed. The passage of ions into and out of the cell through these pores and channels are thus influenced. With varying concentrations of these ions the phase of the osteoclast gradually changes between resorptive and motile.
During the motile phase the cell spreads out and sends out extensions of its membrane in one direction, while retracting its membrane on the opposite side of the cell. During this phase it is not resorbing bone. There are multiple channels or pores in the membrane that determine this activity.
How Calcium Makes A Difference
For the osteoclast the channels that control some of the passage of potassium depend on the concentration of calcium in the cell. When the calcium concentration inside the osteoclast increases enough, the potassium channels open and the cell begins to move. When the concentration is low the cell attaches to the matrix and begins resorbing calcium from the matrix. When the pores take longer to open, the osteoclasts are actively resorbing for a longer time, thus leading to a slow bone loss.
The hydrogen ion is another ion that has a major influence on membrane charge, thus affecting the pores and channels in the cell membrane. Very small changes in the concentration of hydrogen ions (i.e., very small changes in acidity) have large effects on osteoclast activity. This is another mechanism of bone absorption that is affected by the foods we eat.
Foods that are high in potassium, low in sodium and high in the hydrogen ion neutralizers, citrate and bicarbonate, are foods that affect bone density through their effects on the osteoclast cell membrane. To date, the multiple basic science studies of the influence of minerals and ions on osteoclasts are consistent with high potassium foods being the major factor contributing to bone strength.
To find foods high in potassium and low in sodium, look for “table” in the posts listed in the List Of Posts page. These articles will have a list of foods and their potassium content.