Tuesday March 3 2009
The study suggests that milk is one of the best sources of vitamin B12
The Daily Telegraph has reported that “two glasses of milk a day could help protect against Alzheimer's”. The newspaper says that research has shown that “milk is one of the best sources of vitamin B12, which is thought to reduce neurological damage to the brain”. The study is also reported to have found that elderly patients with low levels of vitamin B12 had twice the amount of brain shrinkage found in people with higher levels of the vitamin.
The findings described in the newspaper come from two different studies by the same research group. The findings on B12 levels and brain shrinkage were reported in 2008, while the current study examines how dietary sources of vitamin B12 relate to B12 levels found in the body. While the research suggests that milk and fish are good sources of B12, the study has some limitations and will need to be confirmed by further research.
This study did not look at the effects of milk consumption on brain shrinkage or Alzheimer’s disease, and further research would be needed to determine whether drinking milk can ease these conditions. However, maintaining adequate levels of vitamins through a balanced diet is important for overall health.
Where did the story come from?
Dr Anna Vogiatzoglou and colleagues from the University of Oxford and universities in Norway carried out this research, which was published in the peer-reviewed American Journal of Clinical Nutrition.
The study was funded by a number of Norwegian organisations, including the Norwegian Health Association, the Foundation to Promote Research into Functional Vitamin B12 deficiency, the Research Council of Norway plus the Alzheimer’s Research Trust and the Charles Wolfson Charitable Trust in the UK.
What kind of scientific study was this?
This was a cross-sectional study looking at the relationship between intake of various dietary sources of vitamin B12, and levels of the vitamin in the blood.
Vitamin B12 is found in foods such as dairy products, meat, fish and eggs. Vitamin B12 deficiency is associated with various conditions, such as certain types of anaemia and neurological problems. But most people who eat a mixed Western diet are thought to have sufficient vitamin B12 intake to prevent problems such as anaemia.
However, it is possible that the B12 found in certain foods is absorbed more easily than the B12 in other foods. This study aimed to identify the best food sources of vitamin B12. Another study by this group in 2008 found a link between low vitamin B12 levels in elderly people and brain shrinkage.
The participants in this study were taken from a large population-based study in Norway called the Hordaland Homocysteine Study II (HHSII). The current study included 5,937 participants from two age ranges: 47-49 years and 71-74 years. The participants all provided a blood sample and filled in a food frequency questionnaire (FFQ) about their diet.
Participants also had a health examination and filled in questionnaires about their medical history and lifestyle. The researchers excluded people who did not have their plasma B12 levels measured, provided invalid FFQ answers, or reported having vitamin B12 injections.
The FFQ had been tested in the Norwegian population and found to provide valid data about food intake, including foods containing B12, such as meat. The FFQ asked about frequency and amount of intake of 169 food items over the last year, plus any use of vitamin supplements.
People regularly using at least one daily dose of a supplement containing vitamin B in past year were considered to be supplement users. Vitamin B intake via any supplement was estimated, based on the average supplement contents in 1997-1999, when the study data was collected.
Dietary intake of vitamin B12 was calculated using a computer programme based on the official Norwegian food composition table. The researchers then looked at how well levels of vitamin B12 intake from different dietary sources correlated with levels of B12 found in the participants’ blood.
Results were adjusted for, taking into account participants’ age group, gender, total energy intake, smoking, alcohol intake, intake of other foods containing B12, and use of supplements containing vitamin B. The researchers also looked at whether a high vitamin B12 intake in the diet (defined as intake in the highest 12.5% of measured intakes) reduced the odds of having low vitamin B12 in the blood (defined as less than 200 picomoles per litre).
What were the results of the study?
Blood plasma B12 concentrations were higher in younger men than in older ones, and higher in females than males. Overall, just under 5% of participants were classed as having low levels of vitamin B12 in their blood, with 1% having very low levels (less than 150 picomoles per litre).
Dietary vitamin B12 intake was higher in men and in the younger age group (47-49 years old). Just over 2% of participants had vitamin B12 intakes below Norwegian nutritional recommendations (less than two microgrammes a day). Most vitamin B12 in the participants’ diets came from fish, followed by meat and milk.
Levels of vitamin B12 in the blood showed a link with total levels of vitamin B12 intake in the diet. When looking at specific dietary sources, levels of B12 in the blood showed the greatest link (correlation) with levels of dairy product intake, particularly milk, followed by intake of fish. This meant that individuals with a higher milk and fish intake showed higher levels of vitamin B12 in their blood. Levels of meat intake did not show a significant link with levels of B12 in the blood.
People with the highest levels of vitamin B12 intake in their diet were about a third less likely to have low levels of vitamin B12 in their blood.
What interpretations did the researchers draw from these results?
The researchers concluded that milk and fish in the diet are significant contributors to levels of vitamin B12 in the blood. They suggest that “guidelines for improving vitamin B12 status should take this into consideration”.
What does the NHS Knowledge Service make of this study?
This study suggests that some foods may be better than others at providing vitamin B12 to our bodies. However, there are a number of limitations to consider:
- The study only looked at vitamin B12 levels in the blood at one time point, and this may not be representative of the levels of B12 in their blood over a longer time period.
- Although the food frequency questionnaire has been tested and shown to give reasonable estimates of food intakes, it is likely that there will be some inaccuracy in the participants’ recall of what they ate over a whole year. These inaccuracies could affect results.
- Results may not be applicable in other countries with a different ethnic makeup or different dietary habits. In addition, results may not be applicable in younger age groups (aged under 47 years).
- The link between total dietary vitamin B12 intake and levels of vitamin B12 in the blood was not very strong, with a correlation coefficient of 0.1: a correlation coefficient of 0 would indicate no link, and a correlation coefficient of 1 shows the strongest possible link. This weak correlation suggests that there may be factors other than dietary intake of B12 affecting these results, which may include inaccuracies in the assessment of vitamin B12 intake.
- Although most of the newspapers concentrate on the suggestion that milk can reduce risk of Alzheimer’s disease or brain shrinkage, this study did not assess this possibility. Further research would be needed to determine whether this is the case.
A review of the findings of this and other similar studies would be needed before the findings could be included in nutritional guidelines. However, eating more fish and less meat is in keeping with current thinking about healthy diets. In addition, consuming milk will also help maintain calcium levels and healthy bones and teeth. Ensuring adequate levels of vitamins by eating a healthy balanced diet is important for maintaining good health.