While women who met Nordic whole grain recommendations for years were less likely to develop breast cancer, research has found that not all whole grain foods affect cancer risk in the same way.
Study: Long-term whole grain intake in line with the 2023 Nordic Nutritional Recommendations and breast cancer risk in a population-based cohort of women. Image credit: marilyn barbone/Shutterstock.com
According to a recent study published in european nutrition journalin line with the 2023 Nordic Nutritional Recommendations, women with a long-term intake of at least 90g of whole grains per day had a lower risk of breast cancer than women with much lower intakes of whole grains. The findings also suggest that risk associations vary depending on the type of whole grain foods consumed.
Scandinavian whole grain targets tested against breast cancer
Breast cancer is the most common cancer among women worldwide. This is closely related to hormonal exposure, especially exogenous and endogenous estrogen and progesterone. Some scientists hypothesize that a diet rich in fiber may bind estrogen in the colon, thereby reducing estrogen reabsorption. This reduces its levels in the circulation.
This hypothesis is supported by studies that report a reduced risk of breast cancer in women who consume more fiber. Whole grains are rich in dietary fiber, but studies have shown inconsistent results regarding the association between whole grain intake and breast cancer. This may be partly due to the large differences in the types of grains consumed by different populations and the presence of bioactive and anti-carcinogenic compounds in the same type of whole grains from different sources.
Despite this lack of strong evidence, the NNR2023 guidelines recommend consuming at least 90 g of whole grains per day for good health. In the current study, we sought to estimate how adherence to the latest Nordic Nutritional Recommendations (NNR2023) guidelines for whole grain intake correlates with breast cancer risk, particularly the intake of specific whole grain foods such as oats, wheat and rye.
Comparing breast cancer risk by level of whole grain intake
Researchers looked at data from 36,479 women aged 48 to 83 who participated in the Swedish Mammography Cohort. Dietary intake was assessed using a food frequency questionnaire completed in 1997, which served as the baseline. In 2009, 25,259 of the surviving participants completed the resurvey. This provided an estimate of long-term whole grain consumption.
Researchers grouped participants according to how closely they met NNR2023 whole grain recommendations: low compliance (<45 g/day), partial compliance (45 to <90 g/day), and full compliance (≥90 g/day).
Participants were followed for an average of 16.5 years, during which time 1,979 women were newly diagnosed with breast cancer. The mean age of participants at baseline was 62 years, and 81% were postmenopausal. By comparison, those who developed breast cancer were slightly younger at baseline, with an average age of 61 years.
Researchers examined the association between different levels of whole grain intake and breast cancer risk while controlling for lifestyle and medical history factors. These include age, BMI, smoking, physical activity, alcohol intake, diet quality, menstrual and reproductive history, use of hormone therapy, and family history of breast cancer.
Women who were fully compliant with NNR2023 over time were slightly more likely to have a healthy lifestyle. Crispbread accounted for most of the whole grain intake in all categories.
Higher intake of whole grains lowers breast cancer risk
Women who were fully adherent over time were 22% less likely to be diagnosed with breast cancer than women in the low adherent category. No clear reduction in risk was observed in women consuming moderate amounts of whole grains.
Although there was a trend toward decreased risk for hormone receptor-positive tumors, no significant association was observed for either hormone receptor-positive or hormone receptor-negative tumors. Further analyzes based on baseline data only confirmed the observed association.
Individual whole grain foods showed different patterns
When comparing specific whole grain foods, no single food was clearly associated with overall breast cancer risk. However, although moderate intake of breakfast cereals was associated with reduced risk, suggesting that higher intakes may be associated with lower risk, this association was not consistently statistically significant across models. Multivariable-adjusted models showed that high crispbread intake was associated with an increased risk of hormone receptor-negative breast cancer.
The authors suggest that these differences may reflect variations in fiber composition, bioactive compounds, food processing, or contaminants such as acrylamide in some products, but these possibilities require further study.
Grain-specific compounds may form a link with cancer
Researchers have suggested several ways that whole grains may affect breast cancer risk. Their fiber content may help lower circulating estrogen levels, while their effects on gut bacteria and inflammation may also play a role.
Increased intake of whole grains has been shown to reduce levels of pro-inflammatory mediators such as C-reactive protein and interleukin-6, and improve the composition of the gut microbiota, which promotes the production of immunomodulatory short-chain fatty acids (SCFAs). These SCFAs may help suppress inflammatory processes involved in cancer development. Whole grains also contain bioactive compounds such as β-glucan, which is found in oats and has demonstrated anti-proliferative and anti-mutagenic properties.
Conversely, crispbread is made from whole grain flour and may contain acrylamide, which the International Agency for Research on Cancer (IARC) classifies as a possible human carcinogen. This makes it a major source of this chemical in the Swedish diet, and previous studies have suggested a possible link to hormone receptor-negative breast cancer.
The researchers also highlighted that grains such as oats, wheat, and rye vary widely in fiber composition and phytochemical content. These differences may help explain why different whole grain products have different associations with breast cancer risk. The findings further suggest that treating all whole grain foods as a single category may obscure important differences between specific grain types and products.
strengths and limitations
Strengths of this study include a large population-based cohort and large sample of breast cancer cases, repeated dietary assessment over time using a standardized and well-validated questionnaire, long-term follow-up, nearly complete cancer ascertainment through a national registry, and adjustment for many lifestyle and breast cancer risk factors.
However, this study is observational and cannot prove cause and effect. Dietary intake was self-reported using a food frequency questionnaire, which may result in misclassification errors. Residual confounding by unmeasured factors, such as genetic effects, cannot be excluded.
Future research should explore the benefits of reporting whole grain intake rather than whole grain product intake while accounting for regional differences in whole grain consumption. You should also consider how best to get whole grains into a wide range of foods, including foods with relatively low percentages of whole grains.
Achieving Nordic whole grain targets linked to lower breast cancer risk
Long-term intake of at least 90 g of whole grains per day according to Nordic recommendations was associated with a reduced risk of breast cancer in this cohort of Swedish women. The findings also suggest that a variety of whole grain foods may have a distinct relationship with breast cancer risk, particularly hormone receptor subtypes.
This highlights the need for further research into how specific grains and foods influence cancer development. The results further indicate that future research should carefully consider differences among whole grain foods, rather than treating all whole grain products as a single category.
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Reference magazines:
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Pitt, S., Hakansson, N., Kaluza, J., et al. (2026). Long-term whole grain intake in line with Nordic Nutrition Recommendations 2023 and breast cancer risk in a population-based cohort of women. European Journal of Nutrition. Toi: https://doi.org/10.1007/s00394-026-04013-8. https://link.springer.com/article/10.1007/s00394-026-04013-8
