The science behind Christmas herbs and spices

There are surprising therapeutic benefits in the traditional meals we eat at this time of year

This is the time of year when one particular cookery book comes into its own in the Corrigan household. Amidst the plethora of books by celebrity chefs such as Neven Maguire, Mary Berry, and Delia Smith, one yellowing, disintegrating volume takes pride of place. It served as my wife’s textbook for her Home Economics classes at school and even though I gave her a present of the 2015 facsimile edition of All in the Cooking, she still prefers her heavily annotated original copy.

Its importance at Christmas time lies in the recipes it contains for Christmas cake and pudding, along with the details for making brandy butter, which is one of the few seasonal tasks with which I and my pharmaceutical mixing skills, finely honed in Shrewsbury Road, can be trusted, according to my wife.

Another key recipe is for bread sauce, without which Christmas would not be Christmas in my family. Simply describing it as breadcrumbs mixed with milk that has been flavoured with an onion studded with cloves, bay leaf, a blade of mace, peppercorns, and some grated nutmeg, does not do justice to how delicious it is with turkey, ham, and the traditional trimmings. It even works with gluten-free bread. While enjoying it immensely, my inner natural product nerd is also intrigued by those flavourings and spices and their potential biological effects on humans.

Starting with the onion, which, as everyone knows, can produce more tears than even an Oscar acceptance speech, due to the eye-irritating effects of the amino acid-sulphoxide metabolites that are typical of virtually all Alliums. It is also these molecules, along with polyphenols such as quercetin, that are responsible for the reported anti-platelet, anti-thrombotic, anti-asthmatic, and antibiotic activities, as summarised in a 2015 paper in Critical Reviews in Food Science and Nutrition. Two systematic reviews and meta-analyses, from 2023 in Clinical Nutrition and Food Science and Nutrition respectively, highlighted significant improvements in body fat percentage, BMI, LDL-, HDL-, and total cholesterol, systolic and diastolic BP, and liver enzymes in numerous RCTs [randomised controlled trials], after 12 weeks of supplementation with 300mg per day of onion extract.

Peppercorns are interesting from a pharmacokinetic perspective, because the alkaloid piperine in them enhances the absorption of many pharmacologically active molecules through its ability to inhibit key enzymes such as CYP3A4, P-GP and glucuronyltransferases. The supplement industry relies on piperine to increase plasma levels of poorly-bioavailable compounds, notably curcumin from turmeric. Many of the notorious ‘head shop’ products, including the cathinone-containing ‘bath salts’, incorporated piperine itself or a Piper nigrum extract in order to boost activity. More recently in the US, the Food and Drug Administration reported misuse of piperine alongside poorly-bioavailable loperamide in order to self-treat opioid withdrawal or to achieve euphoria.

Peppercorns are interesting from a pharmacokinetic perspective, because the alkaloid piperine in them enhances the absorption of many pharmacologically active molecules

Most of us know of the mild dental anaesthesia and analgesia associated with the essential oil of cloves, alongside its antimicrobial effect on periodontal pathogens due largely to its eugenol content. Eugenol is also found in the oil from the stars of this year’s show, which are the two spices from the tree Myristica fragrans, or nutmeg. The latter is the seed kernel itself, but there is also the rarer mace described as the reddish (when fresh) aril – a lace-like specialised outgrowth that partially covers the seed.

At harvest, this is removed and dried, when it turns yellowy-orange. A 2023 review in the Journal of Applied Pharmaceutical Science noted that mace extracts had anti-H pylori, anti-inflammatory and antioxidant activity, and were also cytotoxic, but clinical studies are needed. Nutmeg itself has been more extensively studied.

One RCT of a topical product containing both nutmeg and mace essential oils in combination with menthol and methyl salicylate did not show any increased analgesia in patients with painful diabetic nephropathy, even though animal models gave positive results. Also, several animal studies have demonstrated a significant and sustained increase in the sexual activity of male rats and mice (BMC Complementary and Alternative Medicine 2005 & 2015) consistent with the traditional use of nutmegs for managing male sexual disorders in the Indian Unani system of medicine.

Surprisingly, nutmeg has a darker side in terms of its history, and also because of the toxicity of the myristicin that is its main chemical component. In the 1700s, the Dutch East Indies Company conducted a campaign of violence bordering on genocide against the inhabitants of the Banda group of Indonesian islands in order to create a nutmeg monopoly. Further colonial warfare led to its introduction into Grenada by the British.

The toxicity of myristicin is linked to its chemical similarity to the hallucinogenic methoxy-amphetamines. Recent years have seen the publication of numerous reports of intoxication after nutmeg ingestion by young people and children, most recently in Cureus (2023). A 2021 paper in Archives of Disease in Childhood drew attention to a social media trend in which children ingest large quantities (several tablespoons) of powdered nutmeg in order to get ‘high’, resulting in severe agitation and altered consciousness, ranging from delirium to coma.

A phenomenon that was once the preserve of US prison inmates has achieved more widespread notoriety allegedly thanks to social media. The methyleugenol and safrole found in nutmeg oil are listed as genotoxic and carcinogenic, but it is unlikely that the sporadic nature of exposure over Christmas represents a real hazard; however, long-term exposure to larger amounts does raise concerns.

The final spice in the bread sauce is a bay leaf, also known as bay laurel, the oil from which contains eugenol and cineole characteristically found in rosemary and tea tree oil, which probably explains the preservative effect of bay against food-borne microbes such as E coli, listeria, and aspergillus. A 2020 study in the Journal of the American College of Nutrition looked at the effect of drinking a tea made from bay leaves daily for 10 days in healthy volunteers and found a significant increase in HDL-cholesterol but non-significant decreases in LDL-cholesterol and triglycerides. An earlier (2009) trial in type 2 diabetics given powdered leaves in capsule form had reported significant decreases in serum glucose and lipid levels. That Journal of Clinical Biochemistry and Nutrition article also noted an increase in HDL-cholesterol.

There is no doubt that Christmas food is highly calorific, but many of the herbs, spices, and trimmings might help in a small way to reduce the damage to our waistlines. In addition, a 2024 paper in Plants points out that the bay leaf was a Roman symbol of peace and prosperity and that is
what I wish for you and your families this Christmas and for 2026.