A new US study has concluded that Vitamin D has no effect on the overall risk of dying from cancer although higher levels of the vitamin may be linked with a decreased risk of dying from colorectal cancer. This finding contradicts the findings of some other studies.
The study is published in the early online issue of the Journal of the National Cancer Institute and is the work of Dr D Michal Freedman, of the National Cancer Institute in Bethesda, Maryland, and colleagues.
The researchers wrote that:
“To our knowledge, this study is the first to examine the relationship between measured serum vitamin D levels and cancer mortality for selected site and for all sites combined.”
Diet and exposure to sunlight are the main source of vitamin D in the body. Some epidemiological studies have suggested there is a link between higher levels of vitamin D and increased survival or reduced risk of dying from cancer. Also studies on animal and human cells have suggested the vitamin shrinks tumours and triggers the death of cancer cells.
Freedman and colleagues analyzed data on 16,818 people who took part in the third national Health and Nutrition Examination Survey. The participants were aged 17 or older and were followed from between 1988 and 1994 up to 2000. Levels of Vitamin D, or more specifically serum 25(OH)D, circulating in the blood at time of enrollment (baseline) were measured using a process known as radioimmunoassay. Levels of vitamin A were also measured for comparison.
The researchers used a statistical method called Cox regression to look at the links between the circulating vitamin D levels and total cancer mortality (in the whole group and by race/ethnicity, sex, age, and other factors) and other types of cancer.
They also looked at links by collection season since some samples were taken in the south during the cooler months and in the north during the warmer months.
The results showed that:
- There were 536 cancer deaths for 146,578 person-years.
- Total cancer mortality was not linked to vitamin D at baseline in the overall population.
- This was the same for men, women, non-Hispanic whites, non-Hispanic blacks and Mexican Americans.
- There was no interaction between vitamin D levels and season.
- There was no interaction between vitamin D and vitamin A levels.
- Colorectal cancer mortality was inversely linked to higher levels of vitamin D (80 nmol/L or higher of serum 25(OH)D).
- This represented a 72 per cent reduced risk compared with lower levels (lower than 50 nmol/L of serum 25(OH)D).
Freedman and colleagues concluded that: “Our results do not support an association between 25(OH)D and total cancer mortality, although there was an inverse relationship between 25(OH)D levels and colorectal cancer mortality.”
In an accompanying editorial, Drs Cindy Davis and Johanna Dwyer, of the National Institutes of Health, also in Bethesda, Maryland, said there was not information about vitamin D to recommend its use in the prevention of disease and death.
“These findings must be put into the context of total diet and lifestyle. There are many risk factors other than diet for colorectal cancer, and there are many possible dietary risk factors other than vitamin D that have been linked to cancer risk,” they wrote.
“Prospective Study of Serum Vitamin D and Cancer Mortality in the United States.”
D. Michal Freedman , Anne C. Looker , Shih-Chen Chang , and Barry I. Graubard.
Journal of the National Cancer Institute Advance Access published on October 30, 2007.
DOI 10.1093/jnci/djm204.
Written by: Catharine Paddock