One of the first studies to look at effects of vitamin D and cancer risk in
an Asian population

Date:

March 7, 2018

Source:

BMJ

Summary:

High levels of vitamin D may be linked to a lower risk of
developing cancer, including liver cancer, concludes a large study.

High levels of vitamin D may be linked to a lower risk of developing
cancer, including liver cancer, concludes a large study of Japanese adults
published by The BMJ today.

The researchers say their findings support the theory that vitamin D might
help protect against some cancers.

Vitamin D is made by the skin in response to sunlight. It helps to maintain
calcium levels in the body to keep bones, teeth and muscles healthy. While the
benefits of vitamin D on bone diseases are well known, there is growing
evidence that Vitamin D may benefit other chronic diseases, including some
cancers.

But so far, most studies have been carried out in European or American
populations, and evidence from Asian populations is limited.

As Vitamin D concentrations and metabolism can vary by ethnicity, it is
important to find out whether similar effects would be seen in non-Caucasian
populations.

So an international research team, based in Japan, set out to assess
whether vitamin D was associated with the risk of total and site specific
cancer.

They analysed data from the Japan Public Health Center-based Prospective
(JPHC) Study, involving 33,736 male and female participants aged between 40 to
69 years.

At the start of the study, participants provided detailed information on
their medical history, diet and lifestyle, and blood samples were taken to
measure vitamin D levels.

Vitamin D levels varied depending on the time of year the sample was taken,
tending to be higher during the summer and autumn months than in the winter or
spring.

After accounting for this seasonal variation, samples were split into four
groups, ranging from the lowest to highest levels of vitamin D.

Participants were then monitored for an average of 16 years, during which
time 3,301 new cases of cancer were recorded.

After adjusting for several known cancer risk factors, such as age, weight
(BMI), physical activity levels, smoking, alcohol intake and dietary factors,
the researchers found that a higher level of vitamin D was associated with a
lower (around 20%) relative risk of overall cancer in both men and women.

Higher vitamin D levels were also associated with a lower (30-50%) relative
risk of liver cancer, and the association was more evident in men than in
women.

No association was found for lung or prostate cancer, and the authors note
that none of the cancers examined showed an increased risk associated with
higher vitamin D levels.

Findings were largely unchanged after accounting for additional dietary
factors and after further analyses to test the strength of the results.

The researchers point to some study limitations, for example numbers of
organ specific cancers were relatively small. And while they adjusted for
several known risk factors, they cannot rule out the possibility that other
unmeasured (confounding) factors may have influenced the results, making it
difficult to draw firm conclusions about cause and effect.

Nevertheless, key strengths include the large sample size for overall
cancer, a long follow-up period and the large number of blood samples analysed.

The authors say their findings support the theory that vitamin D may
protect against the risk of cancer, but that there may be a ceiling effect,
which may suggest that there are no additional benefits beyond a certain level
of vitamin D.

“Further studies are needed to clarify the optimal concentrations [of
vitamin D] for cancer prevention.” they conclude.

Story Source:

Materials provided by BMJ.
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Journal Reference:

1.   
Sanjeev
Budhathoki, Akihisa Hidaka, Taiki Yamaji, Norie Sawada, Sachiko Tanaka-Mizuno,
Aya Kuchiba, Hadrien Charvat, Atsushi Goto, Satoshi Kojima, Natsuki Sudo,
Taichi Shimazu, Shizuka Sasazuki, Manami Inoue, Shoichiro Tsugane, Motoki
Iwasaki. Plasma 25-hydroxyvitamin D concentration and subsequent risk of
total and site specific cancers in Japanese population: large case-cohort study
within Japan Public Health Center-based Prospective Study cohort. BMJ,
2018; k671 DOI: 10.1136/bmj.k671