The rise in household savings rate in some countries is a risk to growth

In the recent period, the household savings rate has been rising markedly in Germany, France and Japan, and this is weakening domestic demand. How can we interpret this rise in the savings rate? There are several possible explanations: The effect of expected population ageing; The effect of uncertainty about future growth; The effect of very low interest rates on savings if the income effect outweighs the substitution effect