Turmeric and bread make for an unusual breakfast. But when Mark Wahlqvist served the combination to a group of older people in Taiwan, he had high hopes. They had been diagnosed as heading for diabetes, which can affect mental abilities. Having heard that the spice could have cognitive benefits, he wanted to put it to the test.
“The idea that turmeric might be brain-protective is novel,” says Wahlqvist, currently at the National Health Research Institutes, in Taipei, Taiwan.
To those following the latest food trends, however, the spice’s brain-boosting potential is unlikely to raise an eyebrow. It is just one in a long list of turmeric’s supposed benefits that has seen it proclaimed as a cheap and effective superfood. As a result, what once may have been gathering dust in your spice rack is now the star attraction at trendy coffee shops selling “golden lattes”.
Other spices are vying for popularity, too. From cinnamon to saffron, the internet is rife with claims about their healing powers, suggesting that they can help with just about any condition from depression to cardiovascular disease and cancer. Even Hillary Clinton reportedly jumped on the bandwagon. After reading that hot peppers can boost the immune system, she was eating one a day during the 2016 United States presidential election campaign in an attempt to improve her stamina. The question is whether we are swallowing anything more than a load of hype.
The promise of medicinal benefits from spices is rooted in traditional medicine. In holistic Ayurvedic medicine, which has been practised for more than 3,000 years in what is now India, turmeric is mixed with milk as a remedy for colds or made into a paste that is applied as a topical treatment for sprains or inflamed joints. More than 300 herbs and spices are used in Chinese medicine, wherein cinnamon is a familiar remedy for muscle pain and excessive sweating, among other ailments. Spices may be added to food or steeped in liquid as a medicinal drink.
The allure of these therapeutic properties spread as herbs and spices were introduced to Europe from Asia and Africa in the Middle Ages, and blossomed as more immigrants settled in Europe in the 20th century, says Wahlqvist. But in the past few years, as our appetite has grown for functional foods – those with health benefits beyond their nutritional value – spices have reached cult status.
In Europe, imports of spices and herbs have increased by 6.1 per cent annually between 2012 and 2016. Google searches for “turmeric” shot up 300 per cent in the US over this period. And sales of supplements of curcumin, an active ingredient in turmeric, reportedly raked in more than US$20 million in 2014.
Scientists, too, have started to wake up to the idea that there could be something in it.
“If relatively inexpensive components of the diet were to mitigate the effects of diabetes and dementia, for example, that would be a welcome advance,” says Wahlqvist.
The number of studies into herbs and spices has risen dramatically in the past decade, and each week about 50 scientific papers are published on the biological interactions of curcumin alone. Yet despite this rapid accumulation of data, the findings are confusing.
In perhaps the largest study to date, Li Liming, at Peking University, in Beijing, and his colleagues followed 480,000 apparently healthy adults in China for about seven years. They found that those who ate chilli peppers almost every day were 14 per cent less likely to die in that time than those who consumed them less than once a week.
If the effects are real, what is it about spices that makes them so healthy? Many of the claims are based on the idea that they contain powerful antioxidants. As our bodies break down the food we eat, they produce rogue molecules called free radicals that contribute to ageing and disease. Antioxidants are thought to be able to mop these up.
Spices are rich in polyphenols, a group of plant compounds believed to have antioxidant properties. This is what first piqued the curiosity of Elizabeth Opara, at Kingston University, in Britain.
“It seems that when you categorise different foods based on antioxidant capacity, herbs and spices are right at the top,” she says.
Opara and her team wanted to find out whether different cooking techniques affected this antioxidant activity. In lab tests, they looked at herbs and spices, including cinnamon, cloves, parsley, sage and thyme. They found that microwaving, simmering and stewing, which all involve heating a liquid, increased antioxidant action, whereas grilling and frying, which use dry heat, decreased it.
But don’t reach for your golden latte just yet. Later research found that consuming herbs and spices did not increase antioxidant activity in people’s blood.
This highlights one big problem with much of the research into spices: it is often done in the lab, and what looks promising in a cell sample rarely bears out in the human body. Other studies in people look more promising, though.
For their breakfast experiment, Wahlqvist and his colleagues wanted to see whether the quantities of turmeric and cinnamon typically eaten in food might help with memory impairment that develops with prediabetes. Some work suggests that cinnamon can lower insulin resistance, which could help control blood sugar levels and guard against the associated neurodegeneration. In their study, a group of 48 people with prediabetes received one of four breakfasts: 1 gram of turmeric, 2 grams of cinnamon, both spices or a placebo, along with a serving of white bread – a nutritionally inert filler that would allow the researchers to isolate the potential effect of the spices.
Those who ate the turmeric breakfast had improvements to their working memory, tests of which are used to predict cognitive decline, six hours later. There were no memory changes in the other groups.
The fact there seems to be a relationship between the spice and memory does not mean that it is causing the change, however: other factors that weren’t controlled could be at play. And the study only included people who eat a Chinese diet, which could affect results. What’s more, the team doesn’t know whether changes are long-lasting or how turmeric could be having an effect.
Perhaps chemical compounds in turmeric can provide clues. Assessing the effect of spices as food can be complicated by the fact they are consumed in small quantities as part of a wider diet. Gary Small, at the University of California, Los Angeles, and his colleagues homed in on the powers of curcumin supplements. Making up about 3 per cent of turmeric, curcumin has become a buzzword in itself and is widely sold as a dietary supplement. More than 120 clinical trials have tested its effectiveness against numerous conditions, from Alzheimer’s disease to erectile dysfunction.
In a study published this year, Small’s team looked at its long-term effect on cognitive abilities in people middle-aged and older with mild, age-related memory issues. One group of 40 took a pill containing 90 milligrams of curcumin twice a day. Another group received a placebo. Both were given cognitive tests every six months over an 18-month period and some people underwent brain scans.
The team found that the memory and mental focus of those taking curcumin improved significantly, while there was no difference detected in the others. The amount of plaques and tangles of proteins – thought to be a cause of cognitive impairment – in brain regions that modulate mood and memory also fell. “I was pleasantly surprised that it worked in a relatively small sample,” says Small.
He suspects that curcumin could be provoking an anti-inflammatory response. Inflammation is the body’s response to injury or infection, but modern living can make it go awry by constantly triggering the process. This has been implicated in conditions ranging from heart disease to depression.
Reducing inflammation in the brain to ease swelling could allow neural cells to function better. This may be connected to the reduction in tangles Small’s team observed. If so, he thinks curcumin pills could be an alternative for people who struggle to make lifestyle changes, such as improving their diet or exercising more.
“It’s hard for people to change their behaviour,” says Small. “Here we’re just asking people to take some capsules a couple of times a day.”
He and his team now plan to follow up with a larger study to confirm the effect. They also found a modest mood boost in the group given the curcumin, something they would like to probe further by including participants with mild depression. In some cases, plaques and tangles have been observed in people who have low mood but not dementia. “We would like to understand that more,” says Small.
Not everyone is convinced about curcumin, however. Last year, Kathryn Nelson, at the University of Minnesota, and her colleagues, who validate chemicals that could be developed into drugs, published a scathing review of curcumin’s supposed health benefits.
“Curcumin research may have entered the steep section of the hyperbolic black hole of natural products where effort rapidly exceeds utility,” they wrote.
One of the biggest criticisms is what they call the “dark side” of the spice: its effect in so many studies suggests it may be due to false positives. “If a chemical is active in every test, that’s a red flag,” says Nelson. “It means that it might not really be active in any of them.”
When hunting for drug candidates, preliminary lab experiments look at whether a chemical is able to bind to a protein implicated in a disease. Some chemicals give false signals. Curcumin is one of them. For instance, it can disrupt cell membranes, making it seem like it is interacting with proteins on a cell’s surface. In various solutions, it also seems to fluoresce, which is often sought out as a marker of activity. Curcumin has appeared to have an effect in drug screening for many conditions, yet it has never led to a proven treatment.
There are also questions about whether enough of the substance is absorbed into the body to have an effect. “Even when you give people up to 12 grams a day of curcumin, you can’t find it in their bloodstream,” says Nelson.
Human error plays a part, too. Several papers by Bharat Aggarwal, formerly at the University of Texas, laid the groundwork for clinical trials looking at the effect of curcumin in treating cancer, but were later retracted.
As for cinnamon, a review of randomised trials studying its effects on diabetes had to discard most identified studies because of the risk of bias. From the scant studies remaining, it concluded there was no strong evidence of any health benefits.
That doesn’t mean spices are a lost cause – but a lot more evidence is needed before we should take them seriously. And there may be beneficial effects we simply haven’t discovered yet. Take the case of artemisinin, currently the most effective malaria treatment. The Nobel Prize-winning discovery was made by screening 2,000 remedies from Chinese medicine.
Topical uses of spices should have more scope since active ingredients don’t need to be absorbed into the bloodstream to work. Several teams are looking at the potential antimicrobial properties of spices, and even incorporating them into packaging to preserve food. “People are using curcumin as a supplement and that’s not what traditional medicine was doing to start with,” says Nelson.
Besides, there are other good reasons to fall in love with the contents of your spice rack. While they might not live up to their reputation as a cheap and easy panacea, spices have now been added to national dietary guidelines in both the US and Australia that previously focused on staples such as meat, carbohydrates, fruit and vegetables. Why? Adding spices to food is an easy way to cut down on salt, which can raise blood pressure. A diverse diet is widely recommended as the healthiest way to eat and variety, after all, is the spice of life.
Text: New Scientist