2024-05-13 15:50:00
The randomized follow-up, carried out until 2020, followed a seven-year intervention study that ended in 2005. The intervention study examined the effect of daily calcium and vitamin D supplementation on the risk of fracture and breast and colon cancer in postmenopausal women. Taking it led to a moderate increase in hip bone density, but no reduction in the risk of breast and colon cancer. The study was part of the Women’s Health Initiative (WHI), a multicenter landmark study in the United States. In this, strategies for health prophylaxis for older women were researched and continued in various extension studies [1, 2].
Outcome: double-edged sword
The results of the intervention were now updated and re-evaluated by the results from the follow-up period. The data from the National Death Index was also added. The data from 18,176 women in the verum group and from 18,106 test subjects taking placebo were evaluated. The post hoc analysis showed that daily intake of 400 mg calcium and 400 IU vitamin D over a period of 22.3 years reduced cancer mortality by 7% (1817 deaths in the verum group vs. 1943 deaths in the placebo group; hazard ratio [HR] = 0.93; 95% confidence interval [KI] = 0.87 to 0.99). However, concurrent use was associated with a 6% increase in cardiovascular death rate (2621 versus 2420 deaths; HR = 1.06; 95% CI = 1.01 to 1.12). No significant effects were found on total mortality or incidence of fracture, cancer or cardiovascular disease.
Both during the intervention and in the follow-up period, private supplementation of calcium (up to 1000 mg/day) and vitamin D (up to 600 IU/day before 1999 and up to 1000 IU/day following) was not an exclusion criterion. However, the percentage of test subjects who supplemented during the study was largely the same in the verum and placebo groups.
Increase the serum level preventively?
In a subgroup analysis, the test subjects in the verum and placebo groups were divided according to whether or not they had privately taken dietary supplements (including vitamin D and calcium) before the start of the study.
Women in the verum group who had not taken any dietary supplements before the study showed an 11% reduced risk of developing cancer and a 31 and 19% reduced incidence of colon and breast cancer respectively in follow-up, in contrast to women with previous supplements. In women in the verum group without prior supplementation, a 25(OH) vitamin D level below 50 nmol/l was found at the start of the study, which rose above this limit with study supplementation.
According to the authors, these findings indicate that supplementation primarily affects tumor biology in the event of nutrient deficiency. One way to prevent cancer may therefore be to correct the deficiency or increase the 25(OH)-vitamin D serum level above 50 nmol/l.
An increase in cardiovascular death rate might not be shown in this subgroup. This was only noticeable in the women who were in the verum group and had already taken nutritional supplements before the start of the study.
Further studies required
Given the many subgroup comparisons and the neglect of different lifestyles, the authors recommend interpreting the results with caution. The researchers suspect that the causal mechanism for the increased cardiovascular mortality is increased calcification of the coronary arteries caused by calcium, which only appears following a longer period of intake.
Therefore, the additional benefit or harm of vitamin D supplementation in combination with calcium compared to vitamin D alone requires further study [1].
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