Japan's health ministry is warning of a coming "dementia surge." Officials estimate that by 2040 more than 5.8 million elderly people will have the condition -- that's about 15 percent of the total senior population.

Ministry researchers based the estimate on the prevalence of dementia among people aged 65 or older in four municipalities across the country.

They say the number of elderly with dementia will increase by more than 1.1 million over the next 15 years.

What's more, they say over 6.1 million people will have mild cognitive impairment by 2040. People with MCI have memory loss but it doesn't significantly impact their daily lives. However, it often leads to dementia.

More of those with dementia will be living alone. One expert stresses the need for community assistance.

Toyo University Professor Takano Tatsuaki says the general public is going to have to come together to set up systems of support for people with dementia.

He warns there won't be enough professionals to care for everyone.