Table 3.

Keyword co-occurrence frequency (Top 35 in count order, 2001–2021).

Keywords	Count	Centrality	First appearance year
vitamin d	594	0.01	2001
infection	502	0.01	2001
d deficiency	424	0.07	2006
risk	364	0.04	2004
association	356	0.09	2001
expression	226	0.09	2001
disease	223	0.01	2001
d supplementation	211	0.01	2009
vitamin d deficiency	192	0.07	2001
children	181	0.11	2003
prevalence	181	0.02	2007
mycobacterium tuberculosis	158	0.1	2001
risk factor	147	0.01	2002
d receptor	146	0.01	2007
double blind	140	0.03	2010
hiv	130	0	2005
cell	129	0.22	2004
health	126	0	2009
prevention	124	0	2009
respiratory tract infection	121	0.01	2010
vitamin d receptor	121	0.06	2007
25 hydroxyvitamin d	117	0.09	2006
mortality	114	0.05	2006
receptor	94	0.02	2008
adult	93	0.03	2002
pulmonary tuberculosis	91	0.08	2002
immune response	89	0.03	2007
susceptibility	88	0.15	2002
tuberculosis	87	0.03	2004
t cell	87	0.01	2007
supplementation	86	0.01	2008
serum 25 hydroxyvitamin d	85	0.06	2008
inflammation	80	0.04	2010
therapy	79	0.04	2007
calcium	78	0.1	2001