Breast cancer: the importance of vitamin D levels

Women with vitamin D deficiencies at the time of breast cancer diagnosis have higher mortality than those with adequate levels of this vitamin.

This is another vivid illustration of the important role of vitamin D in cancer prevention. Discovered in 1919, just after vitamins A, B and C (hence its name “D”), vitamin D plays an absolutely essential role in the absorption of calcium and the growth of bones as well as in the maintenance of good general functioning of the body.

However, unlike other vitamins, which are obtained through food, most (80-95%) of the vitamin D present in our body is produced by the action of the sun on the skin. UVB rays from light cause a molecule called 7-dehydrocholesterol to convert into vitamin D3, which is then changed by the liver and kidneys to 1,25-dihydroxyvitamin D, which is the active form of vitamin. The important role of the sun in the production of vitamin D obviously poses a problem for the populations of the Nordic countries, which are much less exposed to the sun during the winter season.

Insufficient vitamin D levels in women with breast cancer

Such vitamin D deficiency is dangerous, as multiple studies have shown that this vitamin prevents the development of several types of cancer, including colon and breast cancer. In the latter case, it is interesting to note that the incidence of breast cancer is generally higher in regions far from the equator (and which are therefore less sunny in winter) such as the Scandinavian countries, Canada or New Zealand, compared to regions that are sunny for most of the year (Africa in particular). This protection provided by the sun would be due to a higher concentration of vitamin D in the blood of women living in these regions.

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Vitamin D helps reduce the risk of relapse

A study carried out at the University of Toronto shows such a protective role of vitamin D not only in the prevention, but also in the probability of surviving breast cancer. Researchers measured vitamin D levels in the blood of 512 women who had just been diagnosed with breast cancer and followed the progression of the disease for almost 12 years. Nearly three-quarters of women affected by breast cancer had insufficient blood levels of vitamin D, and nearly half were downright deficient. These women were also more often affected by a more aggressive form of cancer.

Analysis of the mortality of women participating in the study indicates that those whose vitamin D levels at diagnosis were insufficient (below 50 nmol per litre) had twice the risk of cancer recurrence. This increased risk is due to a higher presence of metastases in deficient women compared to those whose vitamin D levels were normal. Vitamin D deficiency makes women affected by breast cancer 73% more likely to die from the disease.

The best sources of Vitamin D

In light of these results, it goes without saying that it is absolutely necessary to increase vitamin D intake to effectively prevent cancer. Moreover, several international experts recommend increasing vitamin D intake from 200 IU to 1000 IU per day to reduce the incidence of several cancers. From May to September, increasing your vitamin D level is easy: simply exposing the face and arms for 10 minutes allows the body to produce some 10,000 IU! However, long exposure to the sun is strongly discouraged because it significantly increases the risk of skin cancer. The sun is therefore a double-edged sword that we must use intelligently if we want to derive the maximum benefit from it while avoiding its harmful effects.

From October to April, however, the reduction in the duration of sunshine makes the situation more complicated and it is necessary to turn to other sources of vitamin D. Certain fish, such as tuna and salmon, contain significant levels of this vitamin. vitamin and are therefore an interesting choice, especially since these foods are also rich in omega-3, essential fats that also help prevent cancer. Supplements containing 1000 IU are also a simple, economical and effective way to increase vitamin D intake.

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Mohr: Relationship between Low Ultraviolet B Irradiance and Higher Breast Cancer Risk in 107 Countries The Breast Journal 14: 255-260.

Goodwin PJ. Frequency of vitamin D (Vit D) deficiency at breast cancer (BC) diagnosis and association with risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC. In: Annual Meeting of the American Society of Clinical Oncology;


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