Cruciferous vegetables, such as cauliflower, broccoli sprouts, cabbage and kale are rich sources of sulfur containing compounds called glucosinolates (1). When glucosinolates hydrolyse (breakdown) they form isothiocyanates which may modulate the expression and activity of the enzymes involved in the metabolism and elimination of carcinogens from the body. They are also known to exhibit a range of activities, including antioxidant and anti-inflammatory (2).
Sulforaphane and Broccoli Sprouts
Sulforaphane [SF] is derived from the glucosinolate isothiocyanate, glucoraphanin. Glucoraphanin is converted into SF when the plant cell walls are ruptured (e.g. by chopping, crushing or chewing). SF is the most potent naturally occurring activator of the Nrf2 pathway (3) which regulates over 200 genes, including those responsible for antioxidant and anti-inflammatory activities. Through the Nrf2 pathway, SF works to block the effects of carcinogens through its ability to switch genes 'on and off' (4). For example; by deactivating carcinogens and increasing their excretion, deactivating genes involved with inflammation, and by activating anti-oxidant genes. As such, it has become well known to reduce your risk of getting cancer.
Cruciferous vegetables are rich in glucosinolates with broccoli sprouts containing a particularly large amount, around 250mg per 100g, and have thus become the centre of focus for much research surrounding cruciferous vegetables and cancer prevention. Broccoli sprouts have 100x more glucoraphanin than the mature broccoli plant (3), meaning they are able to produce more SF and will thus have greater anticarcinogenic effects.
Sulforaphane and Reduced Cancer Risk - Examples
Benzene is a toxic chemical present in the air due to vehicle exhausts, cigarette smoke and industrial emissions. Long term exposure to benzene is known to have damaging effects on the blood by decreasing the number of red blood cells. As such, exposure can cause leukaemia - cancer of the blood forming organs (5). A study illustrated that the consumption of a broccoli sprout beverage led to consistent increases, of up to 50%, in excretion of benzene (6). Other studies have found that smokers who ate more raw cruciferous vegetables per month, than smokers who do not, had a 55% reduction in lung cancer risk (7).
How to Get the Most Sulforaphane out of your Cruciferous Vegetables
Myrosinases are compounds which catalyse the hydrolysis of glucosinolates (8). The cooking of cruciferous vegetables for more than 5 minutes, over 140°C, will inactivate the myrosinases and prevent the breakdown of glucosinolates, therfore inhibiting SF production (1). To optimize your SF intake, lightly steam your vegetables or eat them raw. Alternatively, mustard seeds are rich in myrosinases and studies have shown that adding them to your cooked vegetables can increase the bioavailability of SF (9).
Currently, there are no exact guidelines for SF intake, but many supplements contain around 1000mg. If broccoli sprouts are not available in your local store, buy them online in powdered or pill form. They are also cheap and easy grow at home. If not, eat lots of raw cruciferous vegetables either with a dip, on salad, or blended into a smoothie.