Vitamin D and Calcium Supplementation Decreases Cancer Risk in Older Women
November 1, 2016
Why did they do this study?
40% of the US population will develop cancer in their lifetime. This is not only a major impact to quality of life, but also costs billions of dollars to treat, an estimated $156 billion by 2020.
There are many epidemiological studies that have shown a correlation of certain cancers with latitude, which can then be associated with vitamin D levels. Many scientists have even worked out how adequate vitamin D could be a deterrent to cancer at the cellular level.
In addition, as the population has moved indoors and sun avoidance has been practiced, it has been noted that low vitamin D status is widespread.
Could something as simple as vitamin D and calcium supplementation reduce risk?
What was the study?
The study was a replication of a previous study, published in 2007. This study used more women and a slightly higher vitamin D amount (2000 IU/day instead of 1100 IU/day). The 2007 study showed a 77% reduction in all non-skin cancers in the treatment group (1100 IU vitamin D and 1500 mg calcium/day). In this study cancer was a secondary outcome – so it was important to do another study with cancer as the primary outcome.
Who was allowed to participate in the new study?
Postmenopausal women 55 years of age and older, living independently, from a rural population in Nebraska, with a few exclusions.
2303 participants were assigned randomly to one of two groups. The treatment arm took 1 vitamin D (2000 IU capsule) once a day and calcium carbonate (500 mg/tablet) three times a day. The placebo group had identical placebo pills. Participants in both groups were allowed to take vitamin D (up to 800 IU/day) and calcium (up to 1500 mg/day).
At the beginning of the study, the mean age was 65 years old, and mean vitamin D intake was about 800 IU/day. Their mean vitamin D level was 33 ng/ml, which is relatively high compared to the general US population. (In the 2007 study, the mean was 28 ng/ml.)
What were the results?
After 4 years, 2064 women completed the study. New diagnoses of invasive or in situ cancer were confirmed by pathology reports in 86 subjects (34 in the treatment group, 52 in the placebo group), after excluding any diagnoses during the 1st year.
They excluded cases in the 1st year because it takes some time for vitamin D levels to rise and also it takes a little while for vitamin D to affect cancer formation. This was also noted in the 2007 study – vitamin D levels had an effect on cancer after the first year. In this study, visit 3 corresponded with 1 year of treatment and a table of vitamin D levels shows that the placebo group still had a mean of around 33 ng/ml (31.6 ng/ml), while the treatment group had a mean vitamin D level of 44 ng/ml.
For the remainder of the study the two groups stayed about the same with their vitamin D levels.
Breast cancer was the type of cancer most commonly found, accounting for more than a third of all cancers in both the treatment and placebo groups.
Charts and Percentages
The graph below shows an analysis by treatment group. This graph includes all 4 years of data, but notice how the two groups have virtually the same plot throughout year 1.
When including the year one data, the treatment group had a 30% reduction in all cancers, with a statistical significance, P-value, of .06. When excluding the year one data, the treatment group had a 35% reduction in all cancers, with a P-value, of .047.
The P-value is a probability, it is a percentage. In the first calculation the P-value was .06, which means that there is a 6% chance that this result (30% reduction in cancer in the vitamin D + calcium group) was due to chance – not the actual treatment. In a different wording, that means you are 94% sure it was NOT chance! The scientific community has agreed that P=.05 or less is an accepted amount for study results to have “significance” and anything higher than P=.05 is “not statistically significant.” There is no middle ground, it is black or white.
Note the second calculation had “significance” with a P-value of .047, which means statistics showed that there is a 95.03% chance that the treatment (vitamin D + calcium) was responsible for the 35% lower cancer risk in years 2-4.
By vitamin D level
We find a higher significance level (P-value) when analyzing by serum level. This was also true of the 2007 study. Of special note is the very clear downward trend of the risk.
This analysis concluded that when compared with a vitamin D level of 30 ng/ml, participants with vitamin D level of 55 ng/ml were 35% less likely to get cancer (P=.03). This means that statistics found a 97% probability that the treatment (vitamin D levels greater than or equal to 55 ng/ml) was responsible for a 35% lower risk of cancer.
Adding other data points
GrassrootsHealth combined data for women 55 and older from the GrassrootsHealth D*action cohort (N = 1,135, median serum level = 48 ng/ml) and the cohort from Lappe’s first study (Lappe 2007, N= 1,169, median serum level = 30 ng/ml) and used the pooled cohort to investigate cancer incidence over time (median = 3.9 years). Combining cohorts gave us a wider range of serum levels, more data, and thus improved statistical power. We looked at all invasive cancers combined, excluding skin cancer.
This analysis found a 71% lower risk of all type cancer with vitamin D levels greater than 40 ng/ml as compared to levels less than 20 ng/ml.
What would you do?
If it takes a year for vitamin D to have an effect on your system, when should you start ensuring that your vitamin D level is 50 ng/ml or higher? If you are a parent, when would you start with your child? At 10 years old? As a teen? When they leave the house? Or as a baby – to ensure the healthiest life possible?