The summer sun is our primary source of vitamin D, and previous population studies have suggested that vitamin D may help prevent breast cancer from developing. Danish scientists have looked closer at this relation and found that women from 50 years of age and older who spend a lot of time outdoors – especially between 10 am and 3 pm – have a lower risk of breast cancer. This is important knowledge because it takes years for breast cancer to develop. Vitamin D appears to have a number of different anti-cancer mechanisms, which is why it is vital for us humans to get plenty of the nutrient throughout life.
Breast cancer is the most common cancer among women and we have not yet managed to bend the curve. On the contrary. The good news is that multiple studies have shown how vitamin D prevents cancer by way of different mechanisms. The ultraviolet sunrays (UVB) are our most important source of vitamin D, a nutrient that we synthesize in the skin when we are exposed to rays from a sun that sits high in the sky. But vitamin D deficiencies have become increasingly common due to factors such as spending too much time indoors, fear of sun exposure because of sun awareness campaigns, overuse of sun cream, ageing processes, overweight and diabetes. Also, having dark skin is a limiting factor.
Less sunlight in the middle of the day means less cancer among women older than 50
Previous population studies suggest that vitamin D may prevent breast cancer. In order to find out more about this connection, a group of Danish scientists compared 38,375 women with breast cancer to healthy controls. All women were younger than 70. The scientists looked at professionally active individuals who spend a great deal of their time outdoors, especially in the period between 10 am and 3 pm where the sun is at its highest position in the sky, which is when the body produces the highest amount of vitamin D.
The researchers did not find any correlation between sun exposure and breast cancer in younger women. However, they found a lower risk in women aged 50 years and older who spent most time in the sun. Women who had worked outdoors for 20 years or longer were 17 percent less likely to develop breast cancer after they passed 50.
The study suggests that there is an inverse relation between sun exposure and the risk of developing breast cancer. The Danish study is published in Occupational & Environmental Medicine.
Lack of vitamin D results in a poorer breast cancer diagnosis
Postmenopausal breast cancer patients who lack vitamin D have a poorer prognosis, according to a study of Brazilian women. The study is published in the North-American science journal Menopause. In this study, it was seen that women with insufficient levels of vitamin D in their blood tended to have larger breast tumors and more metastases. Also, they had more lymph node attacks.
Vitamin D deficiency is linked to increased estrogen levels
Lack of vitamin D is also linked to elevated estrogen levels that cause breast cancer cells to grow. An earlier study from Fred Hutchinson Cancer Research Center, Seattle, USA, shows that supplementing with 50 micrograms of vitamin D for one year lowers estrogen levels in the blood and therefore reduces the risk of breast cancer. This even applies to overweight women who often have higher levels of estrogen in their blood.
Vitamin D supplements prevent breast cancer
Supplements of vitamin D are able to both prevent breast cancer from developing and prevent metastases from forming in the lungs, according to a study of mice that is published in Endocrinology. The scientists observed that vitamin D controls certain chemokines (CXCL12/CXCR4) and signal pathways that are involved in the proliferation of breast cancer cells.
Several meta-analyses have demonstrated that high-dosed vitamin D supplements not only lower the risk of getting breast cancer and other cancer forms, they even improve people’s chance of surviving if they are diagnosed with such cancers. This is why it is so important to get plenty of vitamin D throughout life to maintain optimal blood levels of the nutrient at all times.
Vitamin D supplements
As mentioned above, the sun during the summer period is our primary source of vitamin D. We only get negligible amounts of the nutrient from our diet. Health authorities advise all people to take a supplement during the winter period, and certain exposed or vulnerable groups are advised to supplement all year round.
There are different high-dosed vitamin D supplements (20-80 micrograms) on the market. A person’s actual need for the nutrient depends on different factors such as sun exposure, age, skin type, BMI, and chronic disease. EU’s Scientific Committee on Food has established a safe upper intake level for vitamin D that is 100 micrograms per day for adults, including pregnant and breastfeeding women. Vitamin D is a lipid-soluble vitamin. The highest level of absorption and utilization is obtained with vitamin D in oil-filled capsules.
Vitamin D’s anti-cancer mechanisms:
Pedersen JE, Strandberg-Larsen K et al. Occupational exposures to solar ultraviolet B radiation and risk of subtypes of breast cancer in Danish women. Occupational & Environmental Medicine 2021.
The North American Menopause Society (NAMS). Obesity and vitamin D deficiency may indicate greater risk for breast cancer. ScienceDaily 2018
University of California – San Diego. Greater Levels of vitamin D associated with decreasing risk of breast cancer. 2018
De Sousa Almeida-Filho B et al. Vitamin D is associated with poor breast cancer prognostic features. J Steroid Biochem Mol Biol 2017
Jiarong Li et al. Vitamin D regulates CXCL12/CXCR4 and epithelial-to-mesenchymal transition in model of breast cancer metastasis to lung. Endocrinology 2021 March
Nye D-vitamin-anbefalinger til børn og voksne (foedevarestyrelsen.dk)
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