Lack of vitamin D may 'raise dementia risk'

Behind the Headlines

Thursday August 7 2014

Does vitamin D play a role in dementia?

Could more vitamin D reduce our dementia risk?

People lacking in vitamin D have a higher risk of developing dementia report several media outlets, including BBC News and The Independent.

A study found people severely lacking in the sunshine vitamin were twice as likely to develop dementia and Alzheimer's disease compared with people with healthy levels (50nmol/l or more).

The findings are based on a study of more than 1,650 people aged 65 and above who were followed over a period of about six years to see if they developed dementia.

Researchers found the higher the vitamin D deficiency, the higher the risk of developing dementia and Alzheimer's disease.

They found severe vitamin D deficiency (less than 25nmol/l) is associated with approximately twice the risk of developing dementia or Alzheimer's disease.

Moderately low levels of vitamin D (between 25nmol/l and 50nmol/l) are associated with a 50% increase in risk.

This study was able to show an association between low levels of vitamin D and the risk of developing dementia. But it does not prove that vitamin D deficiency causes the disease.

Other factors that can increase the risk of developing dementia, including a poor diet, lack of activity and general poor health, can also cause a low vitamin D level.

More research is needed to establish whether eating vitamin D-rich foods, such as oily fish, or taking vitamin D supplements could delay or even prevent dementia.

 

Where did the story come from?

The study was carried out by researchers from the University of Exeter Medical School in the UK, Angers University Hospital in France, and Florida International University, Columbia University, the University of Washington, the University of Pittsburgh, the Veteran Affairs Ann Arbor Center for Clinical Management Research, and the University of Michigan in the US.

This study used data on people taking part in the Cardiovascular Health Study, a cohort study that aimed to investigate the underlying causes of cardiovascular disease.

It was funded by the UK National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care (CLAHRC) for the South West Peninsula.

The study was published in the peer-reviewed journal Neurology and is free to read on the journal's website.

The news coverage was broadly accurate, with a number of stories including quotes from the researchers and other experts pointing out these results do not demonstrate low vitamin D levels cause dementia – they only show an association.

 

What kind of research was this?

This was a prospective cohort study that aimed to determine whether low levels of vitamin D are associated with an increased risk of dementia and Alzheimer's disease.

Cohort studies can show an association, but cannot show low vitamin D levels cause dementia or Alzheimer's disease. This is because there could be other factors responsible for the link seen. Large clinical trials are required to prove increasing vitamin D levels reduces the risk of dementia.

 

What did the research involve?

The researchers studied 1,658 people aged 65 or older who were taking part in a US-based cohort study that aimed to investigate the underlying causes of cardiovascular disease. None of the participants had dementia, heart disease or stroke at the start of the study in 1992.

Blood samples were collected at the start of the study. Researchers used the samples to measure vitamin D levels. They divided people into three categories:

  • severely deficient (vitamin D concentration less than 25nmol/l)
  • deficient (vitamin D concentration between 25nmol/l and 50nmol/l)
  • sufficient (vitamin D concentration 50nmol/l or higher)

The participants were followed for an average of 5.6 years. The researchers looked at whether these people developed dementia or Alzheimer's disease.

A committee of neurologists and psychiatrists reviewed annual brain function tests, brain scans, medical records, questionnaires and interviews, and diagnosed dementia or Alzheimer's disease according to international criteria set by the National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association.

The researchers compared the risk of developing dementia, including Alzheimer's disease, between people with severely deficient or deficient vitamin D levels and people with sufficient vitamin D levels.

The researchers adjusted their analyses for age, the time of year when vitamin D concentration was measured, education level, sex, body mass index (BMI), smoking status, alcohol consumption and depressive symptoms.

 

What were the basic results?

One hundred and seventy one people developed dementia or Alzheimer's disease during the study. This is equivalent to 10% of the cohort studied.

People with severely deficient or deficient vitamin D concentrations were at an increased risk of developing dementia or Alzheimer's disease:

  • severely deficient vitamin D levels were associated with a 125% increased risk of developing dementia or Alzheimer's disease (hazard ratio [HR] 2.25, 95% confidence interval [CI] 1.23 to 4.13)
  • deficient vitamin D levels were associated with a 53% increased risk of developing dementia or Alzheimer's disease (HR 1.53, 95% CI 1.06 to 2.21)

The researchers also looked at the risk of developing Alzheimer's disease in particular, a common type of dementia. People with severely deficient or deficient vitamin D concentrations were also at an increased risk of developing Alzheimer's disease:

  • severely deficient vitamin D levels were associated with a 122% increased risk of developing Alzheimer's disease (HR 2.22, 95% CI 1.02 to 4.83)
  • deficient vitamin D levels were associated with a 69% increased risk of developing Alzheimer's disease (HR 1.69, 95% CI 1.06 to 2.69)

The researchers repeated their analyses after excluding people who developed dementia or Alzheimer's disease within the first year of the study.

They did this because it has been suggested that people who develop these conditions may change their diet or reduce their outdoor activity, and that might be responsible for the association seen between low vitamin D levels and dementia and Alzheimer's disease.

In this study, the researchers found the association between low vitamin D levels and dementia or Alzheimer's disease remained after the exclusion of people who developed these conditions within one year.

 

How did the researchers interpret the results?

The researchers concluded: "Our results confirm that vitamin D deficiency is associated with a substantially increased risk of all-cause dementia and Alzheimer's disease. This adds to the ongoing debate about the role of vitamin D in non-skeletal conditions."

 

Conclusion

This cohort study of more than 1,650 elderly people has found that over 5.6 years, severe vitamin D deficiency is associated with approximately twice the risk of developing dementia or Alzheimer's disease.

It also found moderate deficiency is associated with a 50% increase in risk compared with healthy levels of vitamin D.

With this being a cohort study, it was not able to show that low levels of vitamin D caused dementia or Alzheimer's disease – it was simply able to show an association.

Other factors that can increase the risk of developing dementia, such as a poor diet, lack of activity and general poor health, can also cause a low vitamin D level.

A further limitation of this study is that the blood samples were only tested for vitamin D levels once. It is not known if any of the participants knew they were deficient and therefore took vitamin supplements during the study period, which could have influenced the results.

Severe vitamin D deficiency can lead to symptoms of lethargy, bone pain, headaches and difficulty concentrating, so it is also conceivable the deficiency was picked up in a number of these people and treated.

More research is needed to establish whether eating vitamin D-rich foods, such as oily fish, or taking vitamin D supplements could delay or even prevent dementia.

Analysis by Bazian. Edited by NHS ChoicesFollow Behind the Headlines on TwitterJoin the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Low vitamin D 'boosts dementia risk'. BBC News, August 7 2014

Lack of vitamin D raises risk of dementia in later life. Mail Online, August 6 2014

Vitamin D: low levels 'can double dementia risk'. The Independent, August 6 2014

Alzheimer's risk doubles with lack of vitamin D - and upping intake could PREVENT disease. Mirror, August 6 2014

Links to the science

Littlejohns TJ, Henley WE, Lang IA, et al. Vitamin D and the risk of dementia and Alzheimer disease. Neurology. Published online August 6 2014

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