Researchers studied over 162,000 people to understand how two simple blood markers—red blood cell variation and vitamin D levels—might predict dementia risk. They found that people with higher red blood cell variation had more dementia cases, while those with higher vitamin D had fewer cases. The study suggests these effects work through changes in blood fats, especially omega-3 fatty acids. This discovery could lead to new ways to prevent dementia by focusing on these blood markers and dietary changes, offering hope for early detection and prevention strategies.

The Quick Take

  • What they studied: Whether two simple blood tests—measuring red blood cell size variation and vitamin D levels—can predict who might develop dementia later in life
  • Who participated: 162,606 people in the UK Biobank study who were at least 50 years old and didn’t have dementia when the study started. Researchers followed them for up to 15 years
  • Key finding: People with higher red blood cell variation had a 5% increased risk of dementia for each unit increase, while people with higher vitamin D levels had an 11% lower risk. These effects appear to work through changes in blood fat levels
  • What it means for you: Simple blood tests you might already get could help doctors identify dementia risk earlier. Maintaining good vitamin D levels and healthy blood fats (especially omega-3s) may help protect brain health, though more research is needed before making major changes

The Research Details

This was a long-term observation study where researchers followed over 162,000 people for up to 15 years. At the beginning, they measured two things in everyone’s blood: red blood cell variation (how different the sizes of red blood cells are) and vitamin D levels. They then tracked who developed dementia using medical records.

The researchers also measured 249 different substances in the blood that relate to metabolism—how the body processes food and energy. They used special statistical methods to see if these blood substances explained why red blood cell variation and vitamin D affected dementia risk.

They adjusted their results for many other factors that could affect dementia risk, like age, education, heart health, and genetic background. This helps ensure the findings about red blood cells and vitamin D are real and not just due to other differences between people.

This study design is powerful because it follows real people over many years and uses actual medical records to identify dementia cases, rather than relying on people’s memories. By measuring blood substances that reflect how the body processes fats and other nutrients, the researchers could explain the ‘why’ behind the connection—not just that red blood cells and vitamin D matter, but how they might affect the brain

This study is reliable because it used a very large group of people (over 162,000), followed them for a long time, and used official medical records to confirm dementia cases. The researchers carefully controlled for many other factors that could affect results. However, the study mostly included people from the UK, so results might be different in other populations. Also, the effects of red blood cells and vitamin D on dementia risk were modest, meaning other factors also play important roles

What the Results Show

The study found two main opposing effects: Higher red blood cell variation was linked to increased dementia risk. For every unit increase in red blood cell variation, dementia risk went up by about 5%. In contrast, higher vitamin D levels were protective—for every unit increase in vitamin D, dementia risk dropped by about 11%.

When researchers looked at blood fat patterns, they discovered that these effects worked through changes in cholesterol and other lipids. People with higher red blood cell variation had more harmful types of cholesterol (specifically cholesterol in very-low-density particles), while people with higher vitamin D had more beneficial omega-3 fatty acids and less saturated fat.

The blood fat changes explained some—but not all—of the dementia risk. About 8.8% of the red blood cell effect and 10.8% of the vitamin D effect were explained by these lipid changes. Omega-3 fatty acids appeared particularly important in both pathways, suggesting they might be a key link between these blood markers and brain health.

The study found that red blood cell variation and vitamin D don’t work against each other—having low vitamin D doesn’t make high red blood cell variation worse, and vice versa. This suggests they affect dementia risk through separate biological pathways. The researchers identified specific blood fat patterns that were most important: cholesterol in small HDL particles and omega-3 fatty acids appeared to be key players in how these blood markers influence dementia risk

Previous research had suggested both red blood cell variation and vitamin D might relate to dementia, but this is one of the first large studies to examine them together and explain how they work. The findings align with earlier research showing that blood fats, particularly omega-3 fatty acids, are important for brain health. This study adds important detail by showing that red blood cell variation and vitamin D may influence dementia through similar metabolic pathways involving these protective fats

The study mostly included people of European ancestry in the UK, so results might differ in other populations. The effects found were modest—meaning red blood cells and vitamin D are just part of the dementia risk picture. The study couldn’t prove that changing these markers would actually prevent dementia, only that they’re associated with risk. Additionally, vitamin D and red blood cell measurements were taken only once at the start, so changes over time weren’t captured

The Bottom Line

Based on this research (moderate confidence): Maintain adequate vitamin D levels through sun exposure, diet, or supplements as recommended by your doctor. Eat foods rich in omega-3 fatty acids like fish, walnuts, and flaxseeds. Get regular blood work to monitor overall health markers. However, these findings suggest potential benefits but aren’t yet strong enough to recommend major lifestyle overhauls based solely on red blood cell variation or vitamin D levels

This research is most relevant for people over 50, especially those with family history of dementia or concerns about cognitive health. People with low vitamin D or other metabolic concerns should discuss these findings with their doctor. This is less immediately relevant for younger people or those without dementia risk factors, though maintaining good vitamin D and omega-3 intake is generally healthy for everyone

If you make changes based on these findings, you wouldn’t expect to notice immediate effects. Brain health changes happen slowly over years. Vitamin D levels can improve within weeks of supplementation, but effects on dementia risk would take years to develop. This is a long-term prevention strategy, not a quick fix

Want to Apply This Research?

  • Track weekly vitamin D intake (through food and supplements) and omega-3 rich foods consumed. Set a goal of 2-3 servings of omega-3 foods per week and monitor vitamin D supplementation if recommended by your doctor
  • Add one omega-3 rich food to your weekly meal plan (salmon, sardines, walnuts, or flaxseeds). If vitamin D is low, start taking a recommended supplement and log it daily in the app to build the habit
  • Review vitamin D and omega-3 intake monthly. If you get blood work done, log your vitamin D levels in the app to track trends over time. Set reminders for annual blood work to monitor these markers alongside your doctor

This research suggests associations between blood markers and dementia risk but does not prove cause-and-effect relationships. These findings should not replace professional medical advice. Before making changes to vitamin D supplementation, diet, or any health regimen, consult with your healthcare provider, especially if you have existing health conditions or take medications. This study was observational and cannot confirm that changing these markers will prevent dementia. Always discuss personalized dementia prevention strategies with your doctor