Table 1. the studies showing the relationship between vitamin D and hair loss.

AGA: androgenetic alopecia; AA: alopecia areata

Publication	Type of study	Year of publication	Number of patients (N=?)	Probability (p=?)	Research question	Conclusion
Fawzi et al. [20]	Case control study	2016	N=20	P=0.000	To assess VDRs in the skin and blood of AA and AGA patients.	Serum and tissue VDR were lower in patients with AGA than controls.
Sanke et al. [21]	Case control study	2020	N=50	P<0.001	To find a correlation between serum vitamin D levels and the severity of AGA.	Significant correlation between vitamin D deficiency and AGA.
Kondrakhina et al. [22]	Cross sectional study	2020	N=50	P<0.001	To estimate plasma element content and vitamin status in patients with AGA.	Multiple micronutrient deficiencies are present in patients with AGA.
Conic et al. [23]	Author manuscript	2019	N=73	P=0.051	To evaluate vitamin D status in scarring and non-scarring alopecia.	Serum vitamin D was low in AGA patients.
Jun Zhao et al. [24]	Case control study	2020	N=777	P=0.0005	To evaluate the serum vitamin D status in Chinese patients with AGA.	Association between serum 25(OH)D levels and AGA in a Chinese population.
Sarac et al. [25]	Case control study	2018	N=58	P=0.01	To determine the role of vitamin D in hair loss	Patients with AGA were vitamin D deficient.
Danane et al. [26]	Longitudinal Follow up	2021	N=50	P value not defined.	To measure the vitamin D levels in men with premature AGA and to demonstrate its relationship with the severity of the disease.	Significant correlation between vitamin D deficiency and the severity of AGA.
El-Tahlawy et al. [27]	Case control study	2021	N=30	P=0.02	To measure serum vitamin D and serum ferritin levels in patients with male pattern hair loss.	Vitamin D was statistically significantly lower in patients with AGA.
Narang et al. [28]	Prospective study	2017	N=22	P<0.009	To study the efficacy of calcipotriol lotion 0.005% in AA and correlate its outcome with serum vitamin D levels.	Hair growth was observed to be better in patients with low serum vitamin D levels.
Nichols et al. [29]	Case series	2017	N=10	For THC: P=0.014 For HMI: P=0.003	To evaluate the effectiveness of a novel oral supplement containing vitamin D.	This novel supplement may be a useful adjunct in the treatment of AGA.
Bilke et al. [31]	Animal study	2006	N/A	N/A	To evaluate if new hair cycle has started in the VDR null mice.	Lack of VDR causes disruption of hair follicle structure during the first catagen resulting in failure of subsequent hair follicle cycling.
Mady et al. [33]	Animal study	2016	N/A	N/A	The role for 1,25-dihydroxyvitamin D3 and/or calcium in hair follicle cycling by evaluation of alopecia in calbindin-D9kknockout pups.	In calbindin-D9kknockout pups, a maternal vitamin D-deficient/low-calcium diet leads to transient non-cicatricial alopecia.