The Vitamin D Deficiency Crisis: 98% of Adults Falling Short

In a recent study conducted in Japan between April 2019 and March 2020, alarming data has emerged concerning the deficiency of vitamin D among adults. Out of the 5,518 participants residing in Japan, a staggering 98% were found to have insufficient levels of vitamin D. Furthermore, this blog aims to shed light on the age-related disparity in vitamin D deficiency, with younger individuals exhibiting a higher prevalence of insufficiency.

Please note that as a personal trainer, I am not authorized to provide recommendations on food choices. The information provided in this article is a summary of my knowledge. For professional guidance on weight control, please seek advice from a registered dietitian.

The Consequences of Vitamin D Insufficiency

bone fracture

Insufficient vitamin D levels can render us more vulnerable to various health issues, including rickets, osteomalacia, osteoporosis, and bone fractures.

Vitamin D plays a crucial role in calcium absorption, making it vital for maintaining healthy bones. However, it is important to note that while an adequate level of vitamin D is essential, excessive consumption can also have adverse effects. Elevated levels of vitamin D in the blood may lead to symptoms such as nausea, arrhythmia, kidney stones, and urinary stones. Striking a balance is key.

Food and Sunshine: Sources of Vitamin D

Obtaining sufficient vitamin D can be achieved through two main sources:

  • Food
  • Exposure to sunlight.

Whether it’s plant-based or animal-based vitamin D, both are effective in meeting our vitamin D needs. This section provides a list of vitamin D-rich foods, including dried wood ear mushrooms, dried shiitake mushrooms, salmon, Pacific saury, dried whitebait, and eggs (both egg white and yolk).

Maximizing Sun Exposure for Vitamin D Synthesis


Sunshine exposure is another crucial avenue for acquiring vitamin D. However, the duration of exposure varies depending on certain factors. Clothing plays a role, as wearing a t-shirt requires less time in the sun compared to wearing a long-sleeve shirt.

Additionally, it is noteworthy that wearing sunscreen, while crucial for preventing excessive sunburn, can hinder vitamin D production. Thus, it is recommended to expose the skin directly to sunlight for an adequate amount of time, considering the advancements in sunscreen quality.


The prevalence of vitamin D deficiency among adults is a matter of concern, as it can have significant implications for overall health. Striving to maintain optimal levels of vitamin D is essential for the prevention of various bone-related conditions. By incorporating vitamin D-rich foods into our diet and carefully managing our sun exposure, we can take proactive steps toward combating this deficiency.

It is recommended to consult with healthcare professionals to determine the appropriate duration of sun exposure for vitamin D synthesis, considering factors such as geographical location and personal circumstances.

Original Source written in Japanese

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