Past posts discussed the large shift in the Japanese diet after the 1950s as refrigeration allowed a move away from salting as a way to preserve foods. This resulted in a drop in their blood pressure and in the number of strokes. However there has been no systematic look nationwide at the effect on the density of bone in the Japanese.
In Finland a similar shift away from sodium toward potassium for different reasons resulted in a dramatic lowering of hip fractures as well as hypertension and strokes. They just recently showed an increase in the bone mineral density in their population. A longitudinal study of bone mineral density (BMD) in Japan would be more evidence concerning the role of high potassium foods in increasing the density of bone.
A study done in 2006 of bone mineral density in Japan was done comparing 4 different diets in Japan. They compared “Healthy” to 3 other types of diet. As in all of these food history questionnaire studies there are many other differences in the diet than the factor in question. And it is difficult to know the level of nutrients consumed, since there are so many ways of preparing food. But when enough studies are done, eventually an understanding can be extracted.
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.
One group that may have been especially interesting to know the sodium content of would have been the Traditional Japanese diet group. The Traditional Japanese group had a large intake of miso soup. Miso is very high in sodium. It would have been helpful to know if their potassium sodium ratio may have contributed to their decreased bone density.
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. It was the only diet with a large amount of processed meat, which is quite high in sodium. They are 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. If you would like to know the potassium sodium ratio of many different American foods, you can click here to find a listing of many posts. To look for a specific food, look for the food group it is in and 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.