Objective: To explore the associations of low serum levels of vitamin B,, a
nd folate with AD occurrence. Methods: A population-based longitudinal stud
y in Sweden, the Kungsholmen Project. A random sample of 370 nondemented pe
rsons, aged 75 years and older and not treated with B-12 and folate, was fo
llowed for 3 years to detect incident AD cases. Two cut-off points were use
d to define low levels of vitamin B-12 (less than or equal to 150 and less
than or equal to 250 pmol/L) and folate (less than or equal to 10 and less
than or equal to 12 nmol/L), and all analyses were performed using both def
initions. AD and other types of dementia were diagnosed by specialists acco
rding to DSM-III-R criteria. Results: When using B-12 less than or equal to
150pmol/L and folate less than or equal to 10 nmol/L to define low levels,
compared with people with normal levels of both vitamins, subjects with lo
w levels of B,, or folate had twice higher risks of developing AD (relative
risk [RR] = 2.1, 95% CI = 1.2 to 3.5). These associations were even strang
er in subjects with good baseline cognition (RR = 3.1, 95% CI = 1.1 to 8.4)
. Similar relative risks of AD were found in subjects with ion; levels of B
-12 or folate and among those with both vitamins at low levels. A comparabl
e pattern was detected when low vitamin levels were defined as B-12 less th
an or equal to 250 pmol/L and folate less than or equal to 12 nmol/L. Concl
usions: This study suggests that vitamin B-12 and folate may be involved in
the development of AD. A dear association was detected only when both vita
mins were taken into account, especially among the cognitively intact subje
cts. No interaction was found between the two vitamins, Monitoring serum B-
12 and folate concentration in the elderly may be relevant for prevention o
f AD.