Vitamin D3 deficiency can increase the risk of certain pathologies or complications. Vitamin D is necessary to make good use of calcium, for example.
In addition, in the case of autoimmune diseases such as type 1 diabetes, Crohn's, arthritis and many others, maintaining adequate levels of vitamin D is an indispensable part of comprehensive treatment, even at a preventive level, due to the importance it has in modulating the immune system.
Now, vitamin D deficiency is more commonly found than it was previously believed, if we take into account that the greatest amount of it is obtained by exposure to the sun. You don't always have 20 minutes a day to absorb a minimal amount of vitamin D, and windows, clothing, sunscreen, living in cloudy places, etc. make it even harder to reach healthy daily amounts.
Finally, there are certain conditions that increase the risk of vitamin D deficiencies. Among them, being an older adult, having brown or dark skin and suffering from gastrointestinal problems.
All of the above highlights the importance of vitamin D3 and consulting with a doctor or specialist in case you require a supplement.