Depression and dementia have both increased greatly over the last generation. Although depression is far more prevalent than dementia, in 2020, 55 million people worldwide were living with dementia. This figure is projected to double every 20 years. By 2030, it is projected that 78 million people will have dementia and by 2050, 139 million people will be living with it. Unfortunately, about every 3 seconds, another person has been diagnosed with dementia.
This increased prevalence of dementia is also associated with a large financial burden. The global cost of dementia is now above 1.3 trillion dollars a year and is projected to rise to 2.8 trillion dollars annually by 2030.[i] Dementia also causes more deaths than breast and prostate cancer combined and is now the seventh leading cause of death in America. One out of every three deaths in seniors is from dementia.
Depression is considered a psychiatric disease, which means it is diagnosed by a constellation of symptoms and not through objective pathological testing. However, dementia is considered a neurological disease, which means it is definitively diagnosed through pathological testing, such as amyloid plaques on brain biopsy or vascular disease of the brain seen on an MRI/MRA of the brain.
Are Depression and Dementia Linked?
These two diseases being so different, why then are they linked? Or is it just coincidental? Association does not necessarily mean causation.
To better clarify this link, Swedish researchers tracked almost 120,000 men and women who had been diagnosed with clinical depression and followed them for up to 35 years and compared them with peers who were not depressed.
Dementia developed in 5.7 percent of those who had depression compared to 2.6 percent of those who were had not been depressed. Depression increased the risk of dementia more than 2-fold. However, people over 50 who had just been diagnosed with depression had a more than 15 times the risk of developing dementia a year later. Even 20 years later the risk of dementia remained higher in those who had depression.[ii]
These same researchers then looked at 25,000 pairs of siblings, in which a brother or sister had depression, but their sibling did not. The sibling who had depression was more than 20 times as likely to develop dementia compared to the emotionally healthy sibling. This risk also remained elevated for over 20 years after the depression diagnosis.[ii]
The risk of dementia was even higher for those diagnosed with severe depression as compared to those who just had mild depression. It is important to note that not everyone who has depression will end up developing dementia, but it begs the question as to why there is such a strong linkage?
Why Is There Such a Strong Link?
I propose that the reason why there is a strong link between depression and the later development of dementia, at least in part, is due to many identical risk factors for both. Oxidized LDL cholesterol and/or hypertension increases the risk of depression and both of the most prevalent causes of dementia (Alzheimer’s disease and vascular dementia). Both depression and dementia appear to have a similar, if not identical, adverse metabolic cause.[iii] This is why diabetes, obesity, smoking, and physical inactivity increase the risk of both depression and dementia.
What Can Be Done?
A diet high in antioxidants can help to prevent depression and anxiety. A diet higher in omega-3 fatty acids can help prevent both diseases and may even help to reverse depression. The algae-based (non-fish), long-chain omega-3 (DHA) has been shown to improve memory in those with “age related cognitive decline” which is really early dementia. The long chains will lower triglycerides which helps metabolism, and along with the long chain EPA, can improve mood in those suffering from depression.
If I diagnose either depression or dementia in one of my patients, I will emphasize the importance of controlling their blood pressure (ideally equal or less than 115/80) and an LDL cholesterol of less than 90. In addition, I will advise that they cut out saturated fat like coconut oil and palm oil and emphasize nuts that have a higher polyunsaturated to saturated fat ratio, such as almonds, walnuts, pecans, and hickory nuts. And I will recommend a low sodium diet by only eating prepared foods that have less milligrams of sodium/serving than calories/serving. Doing this will insure less than 2,000 mg of sodium per day. If you are only eating 1,000 mg of sodium per day, that can lower your systolic blood pressure by 15-20 mm.
I will also recommend plant-based omega-3 fatty acid supplements such as Opti-3 or Algae Omega in addition to eating plant-sources of omega-3 (such as ground flaxseed and chia seed, hemp seed, and walnuts), like our quick and easy Plant-Based Omega-3.
Instead of hoping we don’t get either depression or dementia, why not act today to prevent both diseases? I have many patients that we have screened them for early dementia with the MCI memory test, and when they switch to a plant-based diet and improve their lifestyle for the better, including good cardio exercises daily, the progression of their dementia can be completely halted. If you adopt a healthier lifestyle now, you may also drastically reduce your risk of cognitive decline and experience a happier, fuller life both now and down the road.
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[i] Alzheimer's Disease International. (n.d.). Dementia statistics.
[ii] Holmquist, S., Nordström, A., & Nordström, P. (2020). The association of depression with subsequent dementia diagnosis: A Swedish nationwide cohort study from 1964 to 2016. PLoS medicine, 17(1), e1003016.
[iii] Palmer, C. M. (2022). Brain energy: A revolutionary breakthrough in understanding mental health--and improving treatment for anxiety, depression, OCD, PTSD, and more. BenBella Books, Inc.