Past posts discussed the large shift in the Japanese diet after the 1950s. More widespread use of refrigeration allowed a move away from salting as a way to preserve foods. As a result, Japanese blood pressure dropped, and the number of strokes suffered by the Japanese decreased. However, no one looked at the effect on the density of bone in the Japanese.
For different reasons, a similar shift away from sodium toward potassium occurred in Finland. This resulted in a dramatic lowering of hip fractures, as well as hypertension and strokes. Just recently Finland showed an increase in the bone mineral density in its population. A longitudinal study of bone mineral density (BMD) in Japan would be more evidence supporting the role of high potassium foods in increasing the density of bone.
Bone Mineral Density In Japan
A study done in 2006 compared bone mineral density of those consuming 4 different diets in Japan. The researchers compared “Healthy” to 3 other types of diet. As in all of these food history questionnaire studies, diets differ in more ways than the factor being studied. And it is difficult to know the level of nutrients consumed, since there are so many ways of preparing food. But with enough studies, you can begin to infer what parts of a diet are important.
In this study, the Healthy diet had more fruits and vegetables, and more potassium than the other diets. This population group also had greater density of bone than the other three groups. Sadly, the researchers did not determine the sodium content.
Additionally, it would have been interesting to know the sodium content of the Traditional Japanese diet group. The Traditional Japanese group had a large intake of miso soup. And miso is very high in sodium. It would have been helpful to know if their potassium sodium ratio may have contributed to this group's decreased bone density.
Worst Performing Group
Lastly, the group with the worst BMD was the Western diet. The Western diet in Japan is different than in the West, but it is more similar to a true Western diet than the other 3. Specifically, it was the only diet with a large amount of processed meat, which is quite high in sodium. Consequently, this group is very likely to have had the worst potassium sodium ratio.
So, although the Japanese do not have a longitudinal study of their entire population, as they do in Finland, Japan does provide some evidence that improved BMD is associated with a higher potassium to sodium ratio in the diet.
Would you like to know the potassium sodium ratio of many different American foods? You can click the “Links to Food Potassium Tables” at the top of this page to find a listing of many food tables. To look for a specific food, look for the food group it is in. The table of those foods should have the ratio for the food you are interested in.
1. Dietary patterns associated with bone mineral density in premenopausal Japanese farmwomen. Okubo H, Sasaki S, Horiguchi H, Oguma E, Miyamoto K, Hosoi Y, Kim MK, Kayama F. Am J Clin Nutr. 2006 May;83(5):1185-92.