Summary: Vitamin D linked to a 20% lower risk of cancer in an extensive 16-year study of over 33,000 people published yesterday in a top journal. [This article first appeared on LongevityFacts. Author: Brady Hartman. ]
Higher levels of vitamin D may be connected to a lower risk of developing cancer, concludes an extensive study of Japanese adults published yesterday.
The scientists say their findings support the theory that vitamin D might help protect against some cancers.
Also called the sunshine vitamin, Vitamin D is made by the skin in response to sunlight. This essential vitamin helps our bodies absorb calcium to keep our bones and the rest of our body healthy. A lack of vitamin D can lead to osteoporosis, a condition of weakened bones.
While doctors fully understand the benefits of vitamin D on bone diseases, there is growing evidence that the vitamin may ward off other chronic diseases, including some types of cancer.
However, up until recently, most studies of Vitamin D have been performed on American or European groups, and evidence from Asian populations is limited.
Vitamin D and Cancer
As Vitamin D concentrations can vary by ethnicity, the researchers decided to find out whether similar effects would be observed in non-Caucasian populations. To that end, a Japanese team set out to assess whether vitamin D was associated with the risk of cancer.
The researchers analyzed data from the Japan Public Health Center Prospective Study, involving 33,736 male and female participants between 40 to 69 years old and published their results in The BMJ on March 7, 2018.
At the start of the study, participants provided detailed data on their diet, lifestyle, and medical history and the researchers drew blood samples to measure their Vitamin D levels.
The Vitamin D levels of the study participants varied depending on the time of year, and tended to be higher during the summer and autumn months, and lower in the winter or spring.
After accounting for this seasonal variation, the researchers split the samples into four groups, ranging from the lowest to highest levels of Vitamin D.
The researchers then monitored the participants for an average of 16 years, during which time they recorded 3,301 new cases of cancer.
After adjusting for known cancer risk factors, such as smoking, age, alcohol intake and dietary factors, body weight (BMI), and physical activity levels, the scientists found that a higher level of vitamin D was linked to about a 20% lower risk of all cancers in both the men and women.
The results were even more striking for liver cancer. The researchers linked higher levels of the sunshine vitamin with a 30-50% lower risk of liver cancer, and the causality was more evident in men than in women.
The scientists could not find an association between Vitamin D and lung tumors or prostate cancer. Moreover, the researchers noted that higher Vitamin D levels were not linked to an increased risk of cancer.
The findings of the study remained mostly unchanged, even after accounting for additional dietary factors and performing other analyses to test the strength of their results.
The scientists point out a few limitations of their study. For example, the numbers of organ-specific cancers were relatively small. And while the researchers adjusted for several known risk factors, they cannot rule out the possibility that other confounding factors may have influenced their results, making it difficult to draw firm conclusions about cause and effect.
Nevertheless, the key strengths of the study include a large number of blood samples analyzed, the large sample size for overall cancer, and an extended follow-up period.
The scientists say their findings support the theory that vitamin D may protect against the risk of cancer. However, they add that there may be a “ceiling effect,” in which there are no additional benefits beyond a certain level of Vitamin D. The authors of the study conclude that
“Further studies are needed to clarify the optimal concentrations [of vitamin D] for cancer prevention.”
Vitamin D is essential to our health in other ways besides our bones and is found throughout in the body. For example, our muscles need it to move, and our nerves need it to carry messages. Moreover, the immune system needs the sunshine vitamin to fight off invading pathogens.
Not many foods contain vitamin D, although fatty fish is one of the most abundant dietary sources. Our bodies produce it when our skin is exposed to sunlight and most people who spend a lot of time outdoors are probably getting all the vitamin D they need.
However, they also may be increasing their risk of skin cancer as well.
According to the NIH’s Office of Dietary Supplements (ODS),
“However, despite the importance of the sun to vitamin D synthesis, it is prudent to limit exposure of skin to sunlight in order to lower the risk for skin cancer. When out in the sun for more than a few minutes, wear protective clothing and apply sunscreen with an SPF (sun protection factor) of 8 or more. Tanning beds also cause the skin to make vitamin D, but pose similar risks for skin cancer.”
The ODS recommends that people get their Vitamin D through a healthy diet. However, that may not always be possible. People who live in colder climes with limited sunshine in the winter months – such as the northern US – may not be getting enough Vitamin D. For example, some researchers estimated that as many as one in five residents of northern Europe are not getting enough of the sunshine vitamin. Some health authorities recommend that certain people not getting enough sunlight take vitamin D supplements. And in the US, the Institute of Medicine (IOM) sets recommended dietary intakes for the sunshine vitamin.
Excessive doses of vitamin D can cause health problems, according to the ODS. Vitamin D is fat-soluble, and any excess builds up in the body’s fatty tissue, causing the body to absorb overly high quantities of calcium. An overabundance of vitamin D can result in heart and kidney problems, among other adverse effects.
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Cover Photo:Trifonenko / Getty Images
“Higher Vitamin D levels may be linked to lower risk of cancer.” British Medical Journal. March 7, 2018. Press release in MedicalXpress.
Budhathoki Sanjeev, Hidaka Akihisa, Yamaji Taiki, Sawada Norie, Tanaka-Mizuno Sachiko, KuchibaAya et al. “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; 360: k671.
“Vitamin D Fact Sheet for Consumers.” Office of Dietary Supplements. April 15, 2016
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