The Age of the 100-Year Life, But... | Hiroyuki Ishida, Dean, Graduate School of Health Management
2024.10.22
On Respect for the Aged Day in September, the Ministry of Health, Labour and Welfare announced that the number of elderly people aged 100 or older had reached 95,119. This marks the 54th consecutive year of a record high, with women accounting for 90% of this group. The number of people aged 100 or older first surpassed 10,000 in 1998, meaning it has increased more than ninefold in about a quarter of a century. At our university, Professor Yasumichi Arai (Faculty of Nursing and Medical Care, Graduate School of Health Management) is a world-renowned authority on supercentenarian research, and this field will likely become increasingly important in various aspects in the future. The background to this is Japan's demographic structure. As is clear from the population pyramid, Japan's age structure has two peaks: the baby boomer generation and the second-generation baby boomers. As these two peaks move toward the age of 100 in a sequential push, it is self-evident that the number of supercentenarians will continue to increase. On reflection, Japan's social infrastructure has been swayed back and forth depending on the life stage of these two peaks—that is, the baby boomers and the second-generation baby boomers. When the number of children increased, elementary schools were built; when housing became scarce, large housing complexes and new towns were constructed. Now, the demand for nursing care facilities is rising, and in the future, it will likely become difficult to book crematoriums. This is like the arrival of a swarm of locusts, and what is left after the swarm departs is not ravaged crops, but unused elementary schools, housing complexes, and vacant houses, which in 50 years will likely become nursing care facilities.
Shortly after World War II, the average life expectancy in Japan was 50 for women and 47 for men (according to data from Meiji Life Insurance). While one can imagine the impact of the past great war, the idea of a 100-year lifespan must have seemed like a dream to people at that time. However, now that this dream has come true, it has not turned out to be a paradise. As a price for living longer, many elderly people live with conditions such as knee pain, back pain, dementia, and the need for nursing care (I imagine that before life expectancy increased so dramatically, people died from other diseases before these geriatric syndromes could develop). Research to combat aging is still in its infancy. For example, in addition to age-related conditions (phenomena) like gray hair, cataracts, and hearing loss, in the field of orthopedics, for conditions such as knee osteoarthritis and spinal stenosis, the current reality is that we can only explain to patients that it is an "aging phenomenon" and that they should "please accept it." While there are hopes for the development of new drugs and the application of regenerative medicine, their early practical application is difficult. Therefore, according to my colleague, Professor Takeshi Hashimoto (Sports Medicine Research Center, Graduate School of Health Management) , research has recently shifted its focus to "how to make things last longer."
Degenerative diseases in orthopedics, such as knee osteoarthritis, are often caused by damage to the articular cartilage (= wearing down of cartilage) due to mechanical stress from bearing weight against gravity over many years or from overuse of the joints. Cartilage, which acts as a cushion for the joints, is mainly composed of water, collagen, and proteoglycans, but the latter two are produced by chondrocytes, which make up only about 2% of the cartilage. Unfortunately, articular cartilage has no blood flow, so if chondrocytes are damaged, the repair mechanism does not function. Therefore, to make cartilage last, the only option is to minimize damage and carefully preserve it. So, is it better not to move it? That's not right either. A certain amount of stimulation is necessary to maintain cartilage, and recent research has revealed that the "optimal" stimulation for activating chondrocytes is a strain force of 10–15% and stimulation at 1 Hz intervals. Strain force is like a compression rate; for example, if an object with a thickness of 10 is compressed to 9, the strain force is 10%. 1 Hz means one stimulation per second.
Now, taking the knee joint as an example, the exercise that corresponds to this 10–15% strain force and 1 Hz stimulation interval is said to be brisk walking. Of course, it depends on body weight, but for a 70 kg man, the calculated strain force on the knee during walking is optimal, and one gait cycle is exactly 1 Hz (meaning taking two steps in about one second. In other words, if you walk at a pace of 120 steps per minute, each foot receives one stimulation per second). Learning that the most fundamental human action, "walking," provides the optimal stimulation for cartilage, I was once again struck by the rationality of the human body's design. On the other hand, mechanical stimulation exceeding this level risks damaging the cartilage. For example, climbing stairs is a harmful action for the knees (compared to walking on flat ground, it involves 1.7 times the gravitational acceleration when going up and 4.4 times when going down). Therefore, Professor Hashimoto recommends that I actively use elevators and escalators. I have been in the position of recommending stair climbing to strengthen lower limb muscles, but from the perspective of cartilage protection, it seems desirable to avoid stairs. It is difficult to reconcile these conflicting findings, but at least for women, who have weaker muscles around the knees than men (= more prone to knee instability), it may be better to avoid stairs as much as possible to make their cartilage last longer, even if they don't have knee pain (this is probably more effective than cartilage supplements = my personal opinion). In fact, the male-to-female ratio for the incidence of knee osteoarthritis is 1:4, being more common in women. I often used to get indignant seeing young women casually using station elevators that were originally installed for the elderly and people with disabilities, but in this age of the 100-year life, I've come to feel that perhaps they are the smarter ones.