Sahak
MKA, Kabir N, Abbas G, Draman S, Hashim NH, Hasan Adli DS. The role of Nigella sativa and its active
constituents in learning and memory. Evid
Based Complement Alternat Med. 2016;2016:6075679. doi: 10.1155/2016/6075679.
Black
cumin (BC; Nigella sativa, Ranunculaceae)
seed oil has been used historically as a preventative and restorative medicine.
BC has been reported to have many useful properties such as immunopotentiation,
bronchodilatation, antitumor, antihistaminic, antidiabetic, antihypertensive, anti-inflammatory,
antimicrobial, hepatoprotective, and gastroprotective effects. However, according
to the authors, there is a relative lack of research supporting the use of BC on
the central nervous system, in particular learning and memory. This review
article reports in vitro, in vivo, and clinical studies that support the potential
use of BC to enhance learning and memory.
Constituents
The
traditional effects of BC are mostly attributed to the fixed and essential oils,
especially the quinone constituents, including thymoquinone, which makes up
30-48% of the total quinone compounds. Thymoquinone is neuroprotective in
several in vitro models such as amyloid beta (Aβ)-induced neurotoxicity. The
essential oil also contains thymol, carvacrol, γ-terpinene, and p-cymene, which also have
anticholinesterase and antioxidant effects in vitro, and flavonoids that are
reported to improve learning, memory, and cognition in animal models. The
anticholinesterase activity is consistent with positive effects on learning and
memory, especially following scopolamine administration.
Other
effects of BC in animals include the following:
- Hyperglycemia
is associated with cognitive decline. In rat models, pretreatment with BC
reduced streptozotocin-induced cognitive impairment, restored antioxidant
enzyme levels, ameliorated spatial memory disturbances, reduced oxidative
stress, and normalized the hypothalamus-pituitary-adrenal gland axis.
- In
a rat model of cognitive impairment, thymoquinone improved antioxidant enzyme
levels and spatial learning.
- A
study in rats demonstrated that BC can improve spatial memory performance.
- One
study in rodents showed that BC can decrease anxiety and increase serotonin turnover
in the brain.
- Epilepsy
can cause poor cognition. BC hydroalcoholic extract prevented learning and
memory declines in a rodent model of epilepsy.
- Hypothyroidism
is associated with learning and memory impairments. In neonatal rats,
hypothyroidism was reversed by BC hydroalcoholic extract.
In humans
The
authors very briefly describe two uncontrolled studies in humans. In one study,
executive functions in various memory-related tests such as logical memory,
digit span, letter cancellation, Rey-Osterrieth complex figure, trail making, and
Stroop tests were improved in elderly subjects taking 500 mg/day of a
commercial BC product for nine weeks. In another study, mood was stabilized,
anxiety was decreased, and memory was improved in adolescent male subjects
taking 500 mg/day BC for four weeks. The authors do not mention whether the two
studies were controlled nor do they identify the products used.
The
mechanism by which BC enhances learning and memory is still unknown. However,
the anticholinesterase effect is surely a major component. The authors conclude
that the preclinical data support further research on the potential use of BC
to treat neurodegeneration-related diseases or brain injury affecting learning and
memory.
—Heather S. Oliff,
PhD
Re: Review of Black Cumin for Improving Learning and Memory