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Vitamin D and its importance for the prevention of breast cancer - and after the diagnosis

Vitamin D and its importance for the prevention of breast cancer - and after the diagnosisLow blood levels of vitamin D are associated with an increased risk of breast cancer. Also, breast cancer patients with optimal levels of vitamin D in their blood can expect to live longer than breast cancer patients with low blood levels of the nutrient. But how much vitamin D is needed to prevent the dreaded disease?

Breast cancer is one of the most common cancer forms with Belgium, Denmark, France, and The Netherlands as the four top-ranking countries in the world in terms of prevalence. Although screening methods have improved over the years, the statistics certainly have not. On the contrary. Therefore, we have every reason in the world to focus more on how to prevent breast cancer. Here, our lifestyle and intake of nutrients like vitamin D, selenium, iodine, and omega-3 fatty acids appears to play a vital role, provided we supply our bloodstream and cells with optimal levels of the nutrient.

Vitamin D protects our cells at several different levels

Vitamin D is primarily known for its role in bone health. Nonetheless, all cells in the body depend on vitamin D. In terms of cancer prevention, vitamin D's primary role is its normalizing effect on genes, cells, and tissues. The secondary role of vitamin D relates to insulin levels, cardiovascular system, immune defense, inflammation processes, and other factors, all of which are also important for the way cells thrive.

Did you know that our primary source of vitamin D is the sun, and that women who get exposed to a lot of sunlight are only half as likely to develop breast cancer compared with those who get less sunshine?

Genes determine how well we utilize vitamin D

Vitamin D's influence on breast cancer prevention depends on our genes, especially a cellular vitamin D receptor known as VDR. Women can have different versions of the VDR gene, which determines how effectively vitamin D binds to the cell. This genetic difference alone may enable some women to be better than others at utilizing the vitamin.
Vitamin D's effect in terms of preventing breast cancer is also related to the intake of calcium. A study has demonstrated that a particular version of the VDR gene is associated with lower risk of breast cancer in women who consume large amounts of calcium. Also, it is important to recall that calcium and magnesium work closely together.

As a part of the follow-up treatment of breast cancer women are offered tamoxifen, which is an anti-estrogen. In laboratory studies, vitamin D has been shown to counteract the growth of tamoxifen-resistant breast cancer cells. This, most likely, is a VDR-related mechanism.
There is also evidence suggesting that vitamin D can reduce the amount of circulating estrogen in the blood by reducing a process called aromatase.

Vitamin D counteracts the following, which is related to the development of breast cancer

  • Inflammation
  • Gene activity - including VDR
  • Cell differentiation
  • Cell growth
  • Angiogenesis (the forming of new blood vessels)
  • Circulating estrogen via aromatase

Population studies reveal a correlation between vitamin D and breast cancer

Several population studies have looked at the relation between vitamin D and breast cancer. Most, but not all, studies show that low vitamin D levels increase the risk of breast cancer, while higher levels seem to protect against the disease. Also, there is evidence pointing to vitamin D as having the greatest effect on breast cancer prevention when women synthesize or consume large amounts of the vitamin early in life. Because of this and other factors, scientists have not always been able to prove a direct relation between actual vitamin D levels in the blood and the risk of breast cancer. When individual studies have failed to show that vitamin D supplements have a protective effect on breast cancer, it may be because the amounts that were consumed were not large enough to make a difference. Here are some studies of interest:

  • According to an Italian study, the risk of breast cancer is significantly lower among women who rank in the top-10 group for intake of vitamin D. The same was seen in a Chinese study.
  • A Canadian study links increased sun exposure from the age of 10-19 years to a reduced risk of breast cancer
  • 1,179 post-menopausal women were divided in three groups in a study. One group got a placebo (dummy pill), one group got a calcium tablet, and one group got a pill with calcium and vitamin D. The women were monitored for four years. The researchers observed 20 cancer cases in the placebo group, 17 cases in the calcium group, and 13 cases in the group that got vitamin D and calcium.
  • A study has shown that 2/3 of breast cancer patients have low vitamin D levels in their blood, especially dark-skinned individuals who produce less vitamin D from sunlight. High-dosed vitamin D supplements increased plasma levels of the nutrient, which was not the case with low-dosed supplements. The researchers therefore concluded that normal vitamin pills with 5-10 micrograms of vitamin D are not effective for preventing breast cancer.
  • A laboratory study has shown that the combination of a vitamin D supplement and radiation therapy increased the death of breast cancer cells from 30 to 75 per cent.
  • A Norwegian study revealed that women who were diagnosed with breast cancer during the summer period where blood levels of vitamin D peak, had the lowest risk of dying of their disease. The researchers concluded that the relatively high vitamin D level at the time where the diagnosis was made helped improve the outcome of conventional therapy.
  • A German study found a relation between low vitamin D levels at the time of the breast cancer diagnosis and initiation of the conventional treatment and an increased risk of the disease flaring up again within the next five years.
  • A mouse study has shown that lack of vitamin D increases the growth of bone metastases

How do we get vitamin D?

The sun is our primary vitamin D source, and the amount of vitamin D that we humans are able to synthesize on a hot summer day can easily be between 10 and 100 times greater than the daily reference intake level.
In the northern parts of Europe it is only possible to synthesize vitamin D in the skin during the summer period where the sun sits sufficiently high in the sky. It therefore makes absolutely no sense to encourage people to stay out of the sun or to cover up in the middle of the day. Even though it is possible to get too much sun, we cannot synthesize too much vitamin D, as the synthesis is self-regulating.
It is a good idea slowly to get used to the sun during the spring period. If you are worried about getting a sunburn, limit your unprotected sun exposure to 20 or 30 minutes daily. After that, apply sunscreen if you plan to spend more time in the sun.
In terms of diet, the highest concentrations of vitamin D are found in cod liver and oily fish such as herring, salmon, mackerel, and sardines. Smaller amounts of vitamin D are found in egg yolk, meat, avocado, plant oils, and high-fat dairy products. The amount of vitamin D that we get from our diet is rather limited.

Vitamin D synthesis on a sunny summer day

  • Indoor activities: 0 micrograms
  • Brief lunch break in the sun: 25 micrograms
  • At the beach in bathing clothes: 250-500 micrograms

The listed figures are merely indicative. A human's vitamin D synthesis depends on many factors such as age, skin type, the time of day etc.

Why do we lack vitamin D?

Vitamin D deficiencies have become increasingly common in the past decades as a result of spending too much time indoors, worrying about sun exposure, shying away from fats in our diet, using sun cream, and using cholesterol-lowering medication for extended lengths of time. Also, older people and individuals with dark skin pigmentation produce less vitamin D than others.
Another problem is the rapidly growing number of overweight people and diabetics, who also have difficulty with synthesizing and utilizing vitamin D and who therefore have an increased need for the vitamin.

New threshold levels call for supplementation during the winter period

The lack of vitamin D and the health complications that follow in its wake are far worse than originally believed. The official guidelines for blood levels of vitamin D suggest 50 nmol per liter as being adequate, but according to leading vitamin D experts, it takes as much as 75-100 nmol per liter to provide optimal disease prevention. Although vitamin D levels are determined by means of blood samples, these are no guarantee of proportionally similar levels in e.g. breast tissue. According to Dr. Jens-Erik Beck Jensen, a chief physician at Hvidovre Hospital, it is not realistic to obtain such high levels of vitamin D by following the official dietary guidelines. In fact, more and more researchers recommend vitamin D supplements during the winter period - and they even recommend all-year supplementation to those who fail to get enough sunlight during the summer.

Vitamin D, supplements, and absorption

Vitamin D is lipid-soluble Therefore, we humans are best able to utilize supplements that contain vitamin D in vegetable oil in capsules. Many scientists claim that it is perfectly responsible to consume supplements that provide 30-100 micrograms of vitamin D daily. This is not more than the amount, which our skin is able to synthesize on a sunny summer day.

Facts on breast cancer

  • Even people who stick with the official dietary guidelines, maintain their ideal weight, limit their alcohol intake, exercise, and avoid smoking can get breast cancer
  • Lack of vitamin D is an overlooked risk factor, which we can fortunately correct by means of sun exposure, diet, and the use of supplements
  • Birth control pills and hormone therapy after menopause increase the risk of breast cancer
  • About one in seven breast cancers is caused by excessive alcohol consumption
  • Obesity and physical inactivity increase the risk (possibly because of the influence on estrogen levels)
  • Shift work and working at night increase your risk
  • The risk for Danish women is five times greater than for Chinese and Japanese women
  • Asian women who shift to western diet habits have the same relative risk as other women of developing breast cancer
  • Lack of selenium, iodine, and omega-3 fatty acids also increase the risk


When the body's vitamin D status is too low, it may affect many of those genes that are responsible for protein coding and the regulation of cell division. Over time, this may increase the risk of cancer or make it difficult to recover completely after receiving treatment.


Densie Webb, PhD, RD: Vitamin D and Cancer - Evidence Suggest This Vital
Nutrient may Cut Risk. Today´s Dietitian. 2012

Grant WB et al. The association of solar ultraviolet (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res 2006

Andreas R Raven: Langvarigt skifteholdsarbejde giver dobbelt kræftrisiko. 2013

Pernille Lund. Sund og smuk - hele livet. Ny videnskab 2016

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