I first noticed it on the school run. Every day, a teacher would be stationed outside the classroom door to shepherd the children into the arms of their waiting parents. But one day, as I was about to exchange our usual greeting, my face reddened. I couldn't remember the teacher's name.
So it came as no surprise to read the results of a new study, last month, that said women's brains start going downhill in their 50s - a decade earlier than previously thought. The academics from the University of California found that, on average, the female mind loses up to five per cent of its sharpness between 50 and 60.
Their study, published in journal Plos One, followed more than 2,000 healthy women, aged in their 40s, for 10 years. It found that verbal memory declined by, on average, one per cent every five years, and cognitive processing - including speed of perception and reaction - declined by one per cent every two years.
Nor was I shocked to read their conclusion: that forgetfulness and stress are bedfellows. After all, negotiating the school gates can be fraught with worry, a toxic brew of competitive mothers and agitated offspring.
One comfort, is that that this decline is a perfectly normal feature of ageing. Best of all though, there is hope: it turns out we can hold our mental downfall in check - and even reverse it.
Thanks to a five-year collaboration with the nutritional therapist Alice Mackintosh, I am happy to report that my school run is now back to normal. I first went to see Alice after becoming interested in harnessing the power of food to improve my own mental health, following two serious breakdowns in my thirties.
At the time of the first, in 1997, I was trying to combine the pressure of working life on a national newspaper, with the demands of a young family. My husband Sebastian and I had two children under the age of three - Edward, two, and three month-old George.
One night I couldn't sleep. But with the insomnia came some other alarming symptoms: my heart rate quickened, I felt sick, and my mind was racing. Was I having a heart attack? It turned out to be the start of an anxiety-fuelled depressive episode which saw me briefly hospitalised. I had a second major episode in 2003, and was seriously incapacitated for eighteen months. Both times I was treated mainly with drugs and therapy, and gradually, I began to recover. But it was at that point that I decided to investigate a holistic approach to good mental health. I didn't want to succumb to a third breakdown if I could possibly avoid it.
I was introduced to the healing powers of a change in diet, when I took George, by now aged nine, to a nutritional therapy clinic in west London to treat his eczema. I was delighted when his angry red skin began to heal, after we reduced the amount of dairy and wheat in his diet. But it wasn't until much later that I wondered if food could boost my mental health, and I sought out Alice, who was also interested in the link between food and mood.
I already knew that my mind could become foggy when I felt stressed, and a psychiatrist told me that a person's IQ can drop by 30 points when they are suffering with anxiety. Over the years there have been times when antidepressants and sleeping pills have left me muddled and forgetful.
Might changing my diet help boost my mental clarity?
Our brains consume about 300 calories every day, and the same again at night. This means that good nutrition is extremely important for our mental health and our ability to remember things - names, for example. Alice taught me that a diet containing processed fats, sugar and preservatives may be setting us up for the kind of chronic inflammation that scientists and doctors think may be at the root of low mood, anxiety and depression, as well as poor cognitive function.
Armed with this information, I resolved to eliminate such foods from my life. Instead, I focused on buying 'real foods' for my family, especially vegetables, which studies have shown can boost our mental health. One, by academics at Arizona State University in 2010, found that a vegetarian diet is associated with good moods, While a 2012 German study suggested that plant antioxidants help neutralise free radicals in our bodies, which have been linked to depression.
We started to eat more eggs, unprocessed carbohydrates, nuts, seeds, and natural fats like butter and olive oil. We increased the amount of probiotics and fermented foods like natural yoghurt, sauerkraut and miso paste we consumed to encourage healthy gut flora. Some scientists now think that stress influences our gut bacteria, which in turn can have an impact on our mental clarity. I also boosted the amount of beetroot I eat. This contains nitric oxide, a compound that improves blood flow by relaxing the vessels. There are compelling studies about the mind-sharpening effects of berries and seafood, too.
Most importantly, we ate calmly and mindfully, using the 70 recipes that Alice and I developed together, based on more than 140 nutritional studies.
In addition, Alice taught me that we should drink more water if we want to think straight. "Dehydration is a major cause of brain fog, as well as low mood and lethargy", she says. I've found keeping a jug on the kitchen table helps me remember to hydrate, as well as eating watery vegetables such as cucumber, courgettes, celery, radishes, leafy greens, kiwis, watermelons and grapefruit. It's my go-to remedy whenever I find myself accidentally calling one of our children Sammy... the name of our dog.
While changing my diet has brought all sorts of cognitive benefits (such as ability to remember names - pretty vital in my work as a writer and mental health campaigner) it is not my only 'lifestyle intervention'. As anyone who has started a piece of work after going for a run knows, exercise helps us think straight: one 2016 study from the Netherlands showed that cardiovascular exercise improves memory - as does sex. I've also started to learn, by heart, one poem a day to keep my brain on track. My 80-year-old mother has one of the sharpest minds I know, and her head is stocked full of rhyming couplets.
Now, at 51, I don't have many school runs left. But I'm glad that I've found strategies to make these last few years more endurable, enjoyable and - best of all - memorable.
Foods to tackle brain fog
Eggs, pecans and liver
Choline is a nutrient which plays a key role in a number of bodily functions, including manufacturing a chemical called acetylcholine, which affects our concentration and memory. While egg yolks are the best source, it can also be found in liver, pecans and soybeans.
The king of 'good mood food' is the blueberry. They are a good source of vitamins K and C, as well as fibre, manganese and antioxidants. Scientists are investigating whether they help protect against heart disease and some cancers. I recommend adding berries of all colours to breakfasts, desserts and smoothies.
Salmon and prawns
Eating more seafood could help boost memory. Crab, and other pink and orange seafood such as salmon and prawns contain astaxanthin, an antioxidant that, according to one study, improve dcognitive function when taken as a supplement.
Oily fish, walnuts and flax seeds
Omega 3 fatty acids, found in oily fish like tuna, as well as walnuts and hemp seeds, are another key ingredient to boost our mood, as well as cognitive function. After all, our brain is made up of 60 per cent fat and need a continuous supply - get eating.