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Staying at home endangers bones: Japan experts encourage sunlight exposure

The sun is seen in the summer in Tokyo. (Mainichi/Kenji Yoneda)

TOKYO -- As people in Japan comply with stay-at-home requests and have less opportunity to be exposed to sunlight amid the coronavirus pandemic, experts are sounding the alarm against vitamin D deficiency that can cause bones to weaken.

In Japan, men and women of all generations are said to lack vitamin D. And because the sun's ultraviolet rays are essential for the body to produce vitamin D, experts are advising people to get exposure to appropriate doses of sunlight.

Ultraviolet rays from the sun have UVA and UVB varieties, and the latter causes sunburn while encouraging synthesis of vitamin D, which helps calcium absorption in the intestinal tract. While the volume of UVB rises in May, it hardly transmits through glass or reaches inside rooms when windows are shut.

Hideaki Nakajima, chief researcher of atmospheric physics and chemistry at the National Institute for Environmental Studies (NIES), says, "Young women and older people in a state of vitamin D deficiency face increased risk of bone illnesses. Children in their growth stage are also feared to suffer vitamin D deficiency if they keep themselves at home and play games all the time." He cited a case of a young woman suffering a stress fracture to her spine just by picking up an object inside a room.

Vitamin D deficiency cannot be detected from people's appearances, nor is it noticed by those who have it. Akiko Kuwabara, associate professor of nutritional therapy at Osaka Prefecture University, developed a seven-item questionnaire for Japanese people to grasp their conditions without getting blood tests or other procedures. The seven questions address dietary habits and the frequency in the use of sunscreens, and if people get scores above a certain level, they are highly likely lacking vitamin D.

So how can one boost their intake of vitamin D? The NIES has released on its website rough guidelines for UV exposure time that are enough for vitamin D synthesis under conditions that have little impact on human skin. For example, it is possible to get a day's recommended worth of UV if exposed to sunlight for about 15 minutes in the daytime in May.

"On a sunny day, it is advisable to stay on a balcony or near an open window. It is also good to walk or jog for about 30 minutes in the morning or evening, when UV rays are weak," Nakajima said. When practicing these methods, people are advised not to put on sunscreen. Because UVB reflects off the surface of the ground, however, one can also soak up the rays in the shade. It is also effective to walk while exposing one's palms, which are less vulnerable to sunburn.

There are also vitamin D-rich foods. In particular, it is said to serve one's health to eat salmon, sardines and eels, which have a high vitamin D content, among other items.

(Japanese original by Hitomi Tanimoto, Lifestyle and Medical News Department)

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