Conclusion
Vitamin D plays a crucial role in the body and severe deficiency can cause health problems. Luckily, except the cause is due to underlying health problems, it can the deficiency can often be mitigated by increased sunlight exposure and dietary changes.
References:
[1] https://medlineplus.gov/vitaminddeficiency.html
[2] https://my.clevelandclinic.org/health/articles/15050-vitamin-d–vitamin-d-deficiency
[3] https://www.webmd.com/diet/guide/vitamin-d-deficiency#2
[4] https://www.medicinenet.com/vitamin_d_deficiency/article.htm#what_causes_a_vitamin_d_deficiency
[5] https://www.webmd.com/diet/guide/vitamin-d-deficiency#2
[6] https://www.medicinenet.com/vitamin_d_deficiency/article.htm#what_causes_a_vitamin_d_deficiency