Coumarin is a pleasant-smelling plant constituent and is responsible for the typical woodruff taste and smell. The naturally occurring substance is to be distinguished from synthetic derivatives that are used as drugs to thin the blood, e.g. phenprocoumon or warfarin, and are also abbreviated as "coumarins".

Coumarin is found, for example, particularly in cassia cinnamon varieties, the tonka bean or woodruff. Ceylon cinnamon varieties contain comparatively very small amounts of coumarin. Coumarin was first obtained as a pure substance from the tonka bean. It is also found in grass and clover species (responsible for the typical "hay smell"). Because of its pleasant odor, coumarin is also used in cosmetics.

Coumarin in woodruff

Woodruff (mayweed) is a plant of the rennet genus. Because of its typical aroma, its leaves are used to make syrup and the "Maibowle"; the "green shot" in the "Berliner Weiße" is also woodruff syrup. In fresh plants, coumarin is usually bound to sugar (coumarin glycoside) and is only released by enzymes during drying. The typical woodruff taste and odor therefore only develops during drying from an odorless precursor of coumarin (coumarin glycoside), which is why fresh woodruff should begin to wilt before use.

Coumarin in cinnamon

Cinnamon is one of the oldest spices in the world and is obtained from the dried bark of the cinnamon tree. This is an evergreen small tree of the laurel family. There are hundreds of species. The two most important are the Ceylon cinnamon tree with broad, leathery leaves and the cassia cinnamon tree with narrower, larger ovate leaves. Cassia cinnamon contains about a hundred times higher amounts of coumarin than Ceylon cinnamon. Especially the bark and leaves of the cinnamon tree are used in many foods and refreshments, but also in pharmaceutical preparations as well as in folk medicine. In particular, preparations from the environment of traditional Asian medicine often use cinnamon varieties rich in cumarin. Thus, these products can lead to an unintentional, undesirable coumarin intake.

The dried bark of the cinnamon tree is used for seasoning. This spice can be purchased either ground as cinnamon powder or unground as cinnamon sticks (dried, rolled-up pieces of bark). Enjoyed pure on the tongue, cinnamon tastes slightly bitter. When mixed with sugar, it immediately develops its characteristic aroma ("cinnamon sugar" for desserts). Cinnamon smells pleasantly aromatic. In Western cuisine, cinnamon is used almost exclusively for desserts, hardly ever for salty meals. Especially at Christmas time, cinnamon is used a lot, be it in cinnamon stars, mulled wine or a spicy cinnamon coffee made of warm milk, honey, cocoa, cinnamon and hot coffee. Cinnamon is also used in exotic spicy cuisine, especially in stews of lamb, eggplant, chickpeas and dried fruits.

Coumarin in cosmetics

Coumarin is used in the cosmetics industry as a fragrance in perfumes, shower gels, lotions or deodorants. The substance can be absorbed relatively easily through the skin and can thus lead to increased coumarin uptake when used regularly, especially in leave-on products such as perfumes. Due to its contact allergic properties, it is legally regulated in Regulation (EC) No. 1223/2009(EU Cosmetics Regulation). The presence of coumarin in cosmetic products must be indicated in the list of ingredients in addition to the indication of perfume or aroma mixtures or of herbal preparations from 0.01% in products that remain on the skin or from 0.001% in products that are washed off after application.

Coumarin, when taken in large quantities over a long period of time, can have negative effects on the liver, which can manifest themselves in increased liver values in the blood up to jaundice in sensitive individuals. This effect has only been observed when a drug containing coumarin is administered over several weeks. Coumarin uptake was several times higher compared to foods flavored with cinnamon or woodruff; after discontinuation of the drug, the described effect was reversible. In animal studies, coumarin in very high amounts administered over long periods of time induced cancer in rats and mice. In contrast, there is no evidence of coumarin-induced tumorigenesis in humans.

Maximum levels for coumarin in food are regulated in the Flavor Regulation 1334/2008 in Annex III. It may not be intentionally added to food as a pure substance, but only as a component of spices. As part of official controls, the regulated product groups are checked for compliance with the legal maximum levels.

In industrially or commercially manufactured products, the maximum levels of coumarin in Europe are regulated in such a way that, with normal consumption, there is no risk of the tolerable daily intake (TDI) being exceeded. The daily tolerable intake is 0.1 mg coumarin per kg body weight. With usual consumption of products containing cinnamon, such as classic Austrian pastries or Christmas cookies, no risk of damage to health is to be expected. A higher intake during the Christmas season is generally balanced out when considered over the course of a year, so that no long-term, alarming exceeding of the daily tolerable intake is to be expected.

As part of a focus campaign in 2019, we reviewed the legally permissible maximum level of coumarin in fine baked goods, including traditional and seasonal baked goods, and in breakfast cereal products with cinnamon, as well as a control data collection in non-alcoholic herbal syrups and herbal beverages. Fifty-seven samples from all over Austria were examined. In one sample (spice cookies with cinnamon) the maximum level for coumarin was exceeded.

Overall, a moderate use of cassia cinnamon spice, woodruff leaves and with tonka bean is recommended:

• If a larger amount of cinnamon spice is to be consumed, Ceylon cinnamon, which has significantly lower coumarin levels (about one-hundredth), should be used. To distinguish between cassia and Ceylon cinnamon, in the case of ground spice, look at the imprint on the package. In the case of cinnamon sticks, the cinnamon varieties differ in the thickness of the spice leaves: Ceylon cinnamon has much thinner leaves, similar to a cigar, while cassia cinnamon sticks consist of much thicker leaves.
• Children, for example, should consume semolina porridge or other dishes with no more than half a teaspoon of cinnamon (0.5 g) per day
• Adults should consume a maximum of 3 g of fresh woodruff per day.
• For the preparation of one liter of woodruff syrup should be used no more than about 20 grams of fresh woodruff leaves
• Pay attention to the list of ingredients of cosmetics

The German Federal Institute for Risk Assessment(BfR) and the European Food Safety Authority(EFSA) have calculated a tolerable daily intake(TDI) of 0.1 mg (milligrams) of coumarin per kg of body weight per day. This means that a person weighing 60 kg can consume 6 mg of coumarin per day for the rest of their life without fear of adverse effects. In this context, it is important to consider the sum of the various sources such as cinnamon, woodruff, tonka bean, cosmetics and food supplements when calculating the coumarin intake.

Absorption through woodruff syrup

As mentioned above, a person weighing 60 kg can consume 6 milligrams of coumarin per day without exceeding the TDI value. This corresponds to approx. 3 g of fresh woodruff. The calculations for coumarin and woodruff syrup are based on the following assumptions: the degree of dryness of woodruff leaves dried in the home is about 80 %, the coumarin content of dried woodruff leaves is about 1 % of the leaf weight and the consumption of woodruff syrup should not exceed the tolerable daily intake(TDI) by more than about half to two thirds.

If you prepare woodruff syrup yourself, you should be moderate with the ingredients:

A guideline for preparing drinks with woodruff is 2 grams of fresh woodruff leaves per day: with this amount, a 60 kg person consumes about two thirds of the daily acceptable intake (coumarin is also absorbed from other sources, e.g. cinnamon, breakfast cereals containing cinnamon or cosmetics containing coumarin).

Numerous recipes for making woodruff syrup can be found on the Internet. Most recipes call for a bunch of woodruff leaves, but some also specify the use of 100 grams of woodruff leaves for half a litre of syrup. This is clearly too much: with this mixing ratio, you end up with approx. 200 mg coumarin in half a litre of syrup. If you take a mixing ratio of 1 part syrup: 6 parts water, this results in three litres of ready-to-drink juice: half a litre of this juice therefore contains approx. 30 mg coumarin, which is more than five times the daily tolerable intake.

Intake through cinnamon

In AGES studies, 1,880 - 3260 mg/kg coumarin was measured in Cassia cinnamon, while the highest value in Ceylon cinnamon was 185 mg/kg.

These differences can be explained by botanical differences: Ceylon cinnamon contains only small amounts of coumarin, whereas cassia cinnamon contains much higher levels of coumarin.

There are no regulations for the use of cinnamon spice in the household. As cinnamon has a very strong flavour and the seasoning of food in many households is not based on precise weighing of the ingredients or an exact "recipe", but varies from person to person, it is difficult to judge how much cinnamon is actually added to a dish.

The quantities of cinnamon given in cookery books vary greatly. Compared to other desserts, baked goods from the Christmas season have a significantly higher proportion of cinnamon in their recipes. However, if cinnamon spice is used sparingly in the household, this is generally no cause for concern, as Austrian pastry cuisine is also strongly characterised by the time of year and the season. As the Advent and Christmas season only lasts a few weeks a year, gingerbread and spice cakes are only consumed in large quantities for a short time. This means that cinnamon intake is spread out over the year.

However, calculated TDI exceedances have already been described when large quantities of cinnamon spice are used.