100 Days to a Younger Brain

Maximize Your Memory, Boost Your Brain Health, and Defy Dementia


By Dr. Sabina Brennan, PhD

Read by Dr. Sabina Brennan, PhD

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An easy program of one-a-day exercises to assess your brain health, improve your memory, protect your brain from cognitive decline and slow the effects of dementia

Living a brain-healthy life is not just to reduce the risk of dementia and other serious health issues but also to improve the quality of your life and brain performance now. Investing in brain health will cost you nothing but time and effort — and the brain-healthy recommendations in this book can all be followed for free! Brain health expert Dr. Sabina Brennan’s steps are simple to follow and within your control so can be integrated into daily life with ease over the course of 100 days, including:
  • Creating a sleep profile and plan
  • Assessing your stress levels and targeting specific areas to improve
  • Building and maintaining a social life, mental health, and emotional wellbeing
  • Planning out physical activity and heart-health practices
Dr. Brennan’s assessments and quizzes empowers readers to make informed choices every day about sleeping, eating and lifestyle habits that will benefit all aspects of life, from work to relationships and achieving personal goals. This motivating book proves that you don’t need to understand complicated neuroscience in order to keep your brain healthy, inspiring you to do at least one small thing every day to radically improve your brain health.


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100 Days to a Younger Brain delivers, in clear everyday language, the basics on how your brain works and how you can keep it healthy, and shares the good news that you can boost brain health and change your brain at any age. As you work through this life-changing program, you will complete a series of assessments to show you a clear picture of the current state of your brain health and give you insight into what you are doing right and what needs fixing.

Whether you’ve come to this book because you are concerned about your memory, you fear getting dementia, or simply value your brain and want to look after it, you will find an abundance of practical tips within these pages that can easily be incorporated into your daily life. These down-to-earth suggestions will help to rejuvenate your brain, optimize memory performance, boost brain health, and even build resilience to allow your brain to cope with or compensate for aging, injury, and diseases that affect the brain, including dementia.

Your brain is fundamental to who you are and it supports you in the things you do each and every day. Brain health is not a passing fad and, once you think about it, it’s quite astonishing that up to now we have essentially excluded our most complex, and most important, organ from our health-care routines.

This is not a book about being brainy but it is a book about being smart enough to invest in brain health. We talk about physical health and we talk about mental health. We even talk about dental health and heart health. It just seemed crazy to me that no one was talking about brain health. After all, you need your brain for everything. There isn’t one thing that you can do without your brain. Just as you invest time every day in dental health, I hope that this book inspires you to do at least one thing every day to boost your brain health.

I didn’t go to university until I was forty-two. Six years later I emerged with a degree in psychology, a PhD, and a passion for brain health. As a cognitive neuroscientist1 and a director of a dementia research program in the Institute of Neuroscience at Trinity College Dublin, I was involved in, surrounded by, and exposed to incredible brain research. Thanks in no small part to amazing advances in brain-imaging technology, scientists are making phenomenal progress in terms of our understanding of brain function and diseases that affect the brain.

But something troubled me. Scientists were doing great work but they spent much of their time talking to other scientists about their research at niche conferences and in academic journals, most of which are inaccessible to the general public. Of course, this kind of academic discourse is absolutely essential for scientific progress, but the scientific literature and research on brain health and dementia can be complex and not easy for everyone to follow. That’s why I’ve written this book. It translates scientific jargon into easy-to-understand, practical information to improve your brain health.

100 Days to a Younger Brain will show you how to hold on to important functions like memory into old age. Adopting a brain-healthy lifestyle is like investing in brain capital; by making smart choices you can build reserves that you can cash in at some point in the future when faced with a challenge such as aging, injury, or disease.

Let’s take Alzheimer’s disease.2 There is currently no cure. The Alzheimer brain is shriveled and atrophied3 compared to a healthy brain and is characterized by cell death and tissue loss. Nobody knows for sure what causes this cell death, but abnormal protein clusters called plaques and twisted strands of another protein called tangles are currently the prime suspects.

You’d be forgiven for thinking that having these plaques and tangles in your brain would mean that you would have the symptoms that we commonly associate with dementia—such as memory loss and confusion. But you would be wrong. You can have the disease in your brain and not experience symptoms! And that more than anything inspired me to write this book.

Let me explain. We know from research that the brains of up to 25 percent of people who have sufficient pathology for a diagnosis of Alzheimer’s disease post mortem are clinically intact before death. About one in four people with the pathology in their brain are resilient to the disease. This means that even though they had the disease, the plaques and tangles, they had no perceptible symptoms. In fact, they remained coherent and continued to function as normal up until they died.

We call this resilience “reserve.” Your brain has the capacity for resilience, too, provided you give it a helping hand by adopting a brain-healthy lifestyle. What’s more, you can replenish these reserves across your lifespan.

Consider for a moment Jake and Peter, two fifty-five-year-old men. Jake has high reserve (high resilience) and Peter has low reserve (low resilience). Both begin to develop the pathology of Alzheimer’s disease in their brains at the same time. For illustrative purposes, let’s say that both die at the age of seventy-five.

Peter, the individual with low reserve, will show symptoms of dementia that gradually worsen over the years. The impairment to Peter’s cognitive functioning4 progresses along a gradually declining slope, going from mild through moderate, to severe and ultimately to his death at the age of seventy-five.

In contrast, Jake, the individual with high reserve, won’t manifest any perceptible symptoms. The disease pathology is still progressing in Jake’s brain but his high levels of reserve allow him to cope with and compensate for the physical damage that is occurring in his brain. Let’s say Jake has a fatal accident at seventy-five. When his brain is examined post-mortem he becomes one of the 25 percent who have sufficient pathology in their brain for a diagnosis of dementia but who were clinically cognitively intact at time of death.

Now it is only fair to point out that had Jake not had the misfortune to be run over by an ice-cream van on the way home from his seventy-fifth birthday celebrations his reserves would eventually have been exhausted and he would at some point have manifested dementia symptoms. However, unlike Peter, who had experienced very gradual loss, Jake’s decline would be dramatic and severe. Like falling off a cliff edge. At some point in the future—had he lived—Jake would have experienced a precipitous drop in his cognitive functioning, bypassing the mild and moderate stages.

Reserve is not a “golden ticket,” nor is it a “get-out-of-jail-free card” but if you build it up through brain-healthy choices, you can defer the onset of dementia symptoms and grant yourself more independent years in possession of your mental faculties.

This resilience isn’t just limited to dementia, it can optimize your everyday brain performance and protect your cognitive functions against injury, stroke, and even diseases like multiple sclerosis5 that strike in early adulthood. Your brain also has an amazing ability to adapt and change across your lifespan. This flexibility, which is called neuroplasticity,6 allows you to learn new things, adapt to changes in your life and environment, and also allows you to compensate for disease and injury.

A stroke or “brain attack” occurs when blood flow to an area of the brain is cut off. Spontaneous plastic changes occur in the brain following a stroke that can help the brain to compensate and can contribute significantly to recovery, for example, of movement. The brain compensates for the damage by activating alternative pathways that run parallel to the damaged one. Recovery from stroke involves relearning motor function using the newly activated compensatory pathways. Stroke is the leading cause of acquired disability, and nine out of ten strokes could be prevented by minimizing risk through brain-healthy life choices. There is considerable variability in the extent to which patients recover after stroke. While the reason behind the varied outcomes is not fully clear, lifestyle factors are thought to play a role and you will read more about that in Chapter 1.

This program will also help you to develop brain-healthy habits that could greatly improve outcomes after stroke or brain injury. If you already have a dementia diagnosis or were to develop a disease that affects brain function, such as Alzheimer’s or multiple sclerosis, at some point in your future, following this guide and building a bespoke Brain Health Plan will enable you to minimize your symptoms and support your independence while living with the disease. Brain health matters, especially if you consider that one in three older adults will have a stroke, dementia, or both.

I have a mission in life, and that mission is to vastly increase the number of people who are able to build up their resilience to brain diseases, so they can live happier, more independent lives for very much longer. Like any good book I think that the final chapter of life should be one of the best. I want to get you talking and thinking about brain health. I want you to look after your brain as routinely as you look after your teeth.

100 Days to a Younger Brain will change the way you live, guiding you toward brain-healthy choices, arming you with practical advice that you can implement each day to rejuvenate and optimize your brain performance, build up your reserves, increase plasticity, and reduce dementia risk. Now it’s time to enjoy the good news about brain health.


How To Use This Book

Chapter 1 explains why everyone needs to invest in brain health.

Chapter 2 explains how your brain works and how you can bank reserves to boost brain health.

Chapters 3–8 introduce the program for 100 Days to a Younger Brain, covering the lifestyle factors that are important for brain health: sleep, stress, social and mental activity, heart health, physical activity, and attitude. As you work through each chapter you will complete a series of assessments that will help you to determine your current brain health profile for each of these factors. The information and assessments in each chapter will help you to set goals and devise an action plan to improve your assets and reduce your risks for each of these lifestyle factors. Where a term has a superscript number (e.g., neuroscientist(1)) you will find further explanation of that term beside the corresponding number in the Notes here.

Chapter 3— Days 1–7: Create your sleep profile and plan

Chapter 4— Days 8–14: Create your stress profile and plan

Chapter 5— Days 15 and 16: Create your mental and social profile and plan

Chapter 6— Days 17–23: Create your heart-health profile and plan

Chapter 7— Days 24–30: Create your physical activity profile and plan

Chapter 8— Days 31 and 32: Create your attitude profile and plan

Chapter 9— Day 33: Create your overall Brain Health Profile
Day 34: Build your bespoke Brain Health Plan
Days 35–100: Embed the brain-health habit into your daily life and put your plan into action

Research suggests that it takes on average sixty-six days to introduce a new daily habit, which is why I have allowed that length of time to embed the brain-health habit into your daily routine.

100-Day Diary

Building a daily brain-health habit is critical for success. To help you to do this I have included a 100-Day Diary at the end of the last chapter that you can use to record your brain-healthy actions each day as you work through the program.

You will increase your chances of success if you commit to doing at least one thing each day that is good for your brain health. Set a daily reminder on your phone, on your calendar, or place a Post-it note on your fridge or beside your toothbrush to remind you every day.

Do it now.

Record your actions every day. Completing the diary will help you build a brain-healthy habit.


Invest in Brain Health

“Every man can, if he so desires, become the sculptor of his own brain.”

Santiago Ramón y Cajal

We all brush our teeth every day but most of us never spare a thought for our brains.

How crazy is that?

Of course, dental health is super important because you need your teeth to eat, to speak, and to smile. But you need your brain for everything, and I mean everything. There isn’t one thing that you can do without your brain. You can’t read this book, you can’t turn this page, and you can’t sit down or stand up without your brain. Come to think of it, you can’t even brush your teeth without your brain.

You need your brain for everything, so brain health matters.

Why is brain health a smart investment?

You were obviously a smart kid because you grasped the complex concept of investment at a very young age. Time spent now brushing your teeth reaps future benefits. You developed a dental-health habit that includes daily brushing because you understood that that investment extends the life of your teeth and protects against tooth decay and dental pain in the future. You know that other activities like flossing, dental visits, and diet offer further protection.

However, as a grown-up you come to understand that even if you fastidiously follow your dentist’s advice, your investment doesn’t come with an absolute guarantee, but rather reduces the risk of pain and delays the onset of decay. Chances are, by the time you reach my age you will have had a couple of fillings and may even need some major work on a crumbling tooth or two. Nonetheless, you know that your teeth are in far better shape than they would have been without daily brushing.

The same applies to brain health.

Certain activities offer protection against decline in brain functions in later life, while some lifestyle choices increase your risk of developing diseases that affect brain function, such as Alzheimer’s disease and other dementias. The important take-home message is that key lifestyle changes and activities that reduce risk or offer protection can easily be incorporated into your daily routine.

As is the case with dental health, having a good brain-health habit is not an absolute guarantee but there is plenty of evidence to suggest that it is definitely a worthwhile investment, especially if you fancy holding on to important cognitive functions such as memory for as long as possible. Maintaining and optimizing brain health will allow you to maximize your overall ability and independence.

Your brain is unique

Your brain allows you to think, to feel, to plan, to love, to laugh, to remember, and lots more besides. But that’s not all; your brain also controls your senses and other parts of your body, including your muscles, organs, and blood vessels. Despite this brilliance you carry it around in your skull without giving it a second thought.

Scientists used to think that the brain was fixed, set like concrete, but we now know that the brain is constantly changing, sculpted by behaviors, experiences, and life choices. One of the big things you can do to help your brain is to adopt a brain-healthy lifestyle.

Your brain is unique, crafted by the experiences that you offer it and the demands that you place on it each and every day. Your brain is a dynamic organ that not only influences your behavior but is also influenced by your behavior. What you do or don’t do influences how well your brain functions now and how resilient it can be when faced with future challenges. Your brain is constantly changing and it is your behaviors and your experiences that shape it.

Your brain is plastic—not credit-card plastic but pliable like putty. This neuroplasticity is a fundamental feature of the human brain. It’s not exclusive to humans but the human brain does appear to excel at adaptation. While genetics7 determine brain size in humans and chimpanzees, the human brain is more responsive to environmental influences, allowing it and its behavior to constantly adapt to changes. We tend to afford a lot of importance to our genes, but lifestyle and life experiences are critical to determining the shape of the brain, how it grows, and how it evolves. You can change your brain through experience. Learning can shape it rather like exercising can shape your muscles.

Accumulate information

When it comes to improving your finances, one of the best steps you can take is to improve your financial knowledge. You could do this by acquiring an understanding of financial concepts and risks as well as opportunities for investment. Gaining knowledge about yourself and your current finances and assets will also help inform your financial decisions and help maximize the return on any investment that you make. A good investment plan will acknowledge your unique needs, allowing you to live well now, plan for your future, and have choice and resilience built in should times get tough.

The same applies to improving your brain health. By reading this book you are taking a very important first step by increasing your knowledge of neuroscience, of dementia risk, and of opportunities for investment in brain health. By completing the questionnaires and diaries throughout the book, you will accumulate important information about yourself, your current habits, your assets and risks. This personal information will help to inform your choices and decisions to bring focus to your investment in brain health, while helping to minimize dementia risk and maximize the return on your investment. In this book you will pull together all of that information to create an honest and personal Brain Health Profile that will inform your initial plan and your longer-term brain-health investment strategy.


Your Brain Health Profile is a bit like a financial portfolio. Good financial advice recommends diversification to help manage risk. There is no “one-size-fits-all” approach to financial investment. Advisers recommend creating an investment mix based on your financial goals, current financial situation, the timeline you are working within, and the amount of risk you can tolerate. They encourage diversity among and within different types of stocks, bonds, and other investments. Diversification doesn’t come with any guarantee of success, but the investment mix allows you to potentially offset some of the impact if one aspect of your portfolio declines or performs poorly.

The recommendation for diversification also applies to brain health. A “one-size-fits-all” plan won’t wash for brain health either. You need to create a brain-health investment mix that is based on your personal goals, your current brain-health situation, the timeline that you are working within (your age, your life stage), and the amount of risk factors that you have and can modify. I encourage diversity among and within different types of brain-healthy investment categories, too. In addition to building a mix of investments across sleep, stress management, social engagement, mental stimulation, heart health, physical activity, and attitude, you also need to have variety within these investments. For example, within physical activity you need to exercise aerobically, strengthen muscles, work on balance, and sit less.

Investing widely is investing wisely

Brain-health investment doesn’t come with a guarantee that you won’t develop dementia but it may help to defy it by offsetting some of the impact that the disease can have on your memory and your ability to sustain an independent life. While there are no guarantees when it comes to dementia in the broader sense, your return on brain-health investment will be handsome, rewarding you in multiple ways across your life. Through daily brain-healthy choices you will gain a sense of rejuvenation and greater satisfaction with life. You will also enjoy individual payoffs and fringe benefits in each of your investment categories, including better heart health, sounder sleep, more laughter, and sharper thinking and memory. When it comes to brain health, investing widely is investing wisely.

Regular check-ups

Financial advisers will also recommend giving your portfolio a regular check-up, at the very minimum once a year or any time your financial circumstances change significantly—such as if you lose your job or gain an inheritance. Regularly checking and updating your Brain Health Profile is also sound advice. Brain health is a long-term investment.

The Brain Health Plan that this book will help you to develop is the first step in a long-term strategy that aims to improve your brain health one day at a time. Regularly revisiting and updating your Brain Health Profile and Brain Health Plan will allow you to track your progress, take account of changing circumstances, and let you see whether you need to rebalance your “asset” mix or reconsider some of your individual investments.

Nothing to lose and everything to gain

Over the course of the next 100 days you will identify your brain-healthy habits and any behaviors that need fixing because they may be barriers to brain health or risk factors for dementia. You have nothing to lose and everything to gain. When it comes to brain health it is entirely within your power to transform your debts into assets by making conscious brain-healthy choices and simple changes to your daily life.

Brain health is for everyone

Whether you are embarking on retirement, are a student starting out in life, or at some point in between, this book aims to convince you to invest in brain health now. You possess an amazing resource inside your head: your brain is more complex than anything money can buy. Your brain is invaluable. It is the greatest gift you will ever receive, so treasure it, nurture it, and stimulate it so that you can reach your full potential throughout your entire life.

It’s never too early or too late to invest in brain health.

Everyone with a brain needs to consider brain health.

Take action now

Your brain is shrinking. From our thirties onwards we lose a little brain volume8 each year through a process called “atrophy”; hit sixty and the rate of that atrophy accelerates. But all is not lost, this book explains how living a brain-healthy life may help you to counteract atrophy and maintain brain volume.

The life choices that we make and the experiences that we have, even as children, can increase our risk of developing diseases that impair cognitive function in later life. Like most late-life disorders, the determinants of Alzheimer’s disease and other dementias stretch right back across the lifespan. The following chapters explain that many of these determinants are modifiable, which means that you can take action now to reduce risk later.

Even a child’s brain will struggle to develop normally in the absence of a stimulating, nurturing, brain-healthy environment. The experiences that we have in early life and those that we give our children impact on their brain health and brain development, affecting not only how their brain functions in childhood but how well it serves them across their entire lives.

The teenage brain goes through a dramatic period of neural reorganization. Neuronal networks9 strengthen with use and unused networks are pruned as the brain matures. Teenage years can be a stressful time and parts of the brain involved in memory function are particularly vulnerable to stress. Adolescence represents an opportune time to condition healthy functioning of this part of the brain through brain-healthy life choices that have the potential for long-lasting positive impact.

A sense of invincibility may blind young adults to the need to invest in their future selves. The earlier the investment in brain health begins, the bigger the rewards. While protection against late-life diseases may not be a priority or even make the radar of young adults, none of us can predict whether we might sustain a brain injury in an accident or while playing sport. Healthier brains are more resilient and have a better chance of bouncing back from or compensating for such setbacks. The time to think about brain health is now.

Even if you have been in possession of a brain for more than sixty years, it will continue to change. The traditional adage is, quite frankly, wrong—you can teach an old dog new tricks. Living a brain-healthy life that is challenging and engaged is critical for cognitive function, especially as we now clock up more years than our ancestors. The quality of those extra years can be enhanced through brain-healthy choices.

Investing in brain health will cost you nothing but time and effort. The brain-healthy recommendations in this book can all be followed for free. That doesn’t mean that they are easy, although some are, but they are within your control and can be integrated into your daily life.

Prevent and optimize

When we asked people across Europe what they feared most about growing old they answered—losing their memory and their independence. They also said that dementia was the disease that they feared most. Sadly, their fears aren’t unfounded. While people are living longer, failing mental function frequently impairs the quality of those extra years. Cognitive decline has emerged as one of the greatest health threats of later life.

Failing mental function is the single biggest obstacle to independent living and to the social integration of older people. Cognitive impairment that does not reach the threshold for dementia diagnosis is not only associated with increased risk for progression to dementia, but also increased health-care costs, neuropsychiatric symptoms, and disability.

Brain health is not just about prevention, it is also about optimization. Living a brain-healthy life will not only help reduce dementia risk and maintain memory function in the future, but will also optimize brain performance in the here and now, enhancing the quality of your life today. Even if you already have a diagnosis or are experiencing memory impairment, making brain-healthy choices will help to optimize your brain function.

Aging and dementia


On Sale
Jan 14, 2020
Hachette Audio

Dr. Sabina Brennan, PhD

About the Author

Dr. Sabina Brennan is a research psychologist and award-winning science communicator. She currently works as a Research Assistant Professor in the Institute of Neuroscience at Trinity College Dublin. Her scientific research focuses on understanding dementia risk and protective factors to establish how decline in cognitive function might be prevented or delayed.

Learn more about this author