Vitamin A is important for good vision and the health of the retina, immune health, cognitive function, the health of your baby yet to be born, the health of your skin, your gut, your bones, and your nerve cells right down to the healthy expression (turning on and off) of your genes.

Ready formed vitamin A is found in animal produce such as butter, milk, eggs and is especially high in liver. Vegans rely on converting certain carotenoids like α-carotene and β-carotene into vitamin A. However, 45% of us have a genetic variation on the BCMO1 gene that results in poor conversion of beta-carotene, This may be due to more frequent consumption of liver in our evolutionary past which made the conversion of carotenes unnecessary. We will also make less vitamin A if we drink alcohol or have low thyroid function, insulin resistance, gut dysbiosis (an imbalance in the gut flora), poor bile acid production, bacterial infection, low stomach acid production or coeliac disease. This may sometimes reveal itself as flecks of yellow-orange pigmentation of the skin on the palms of the hands due to the buildup of the carotenes which have not been converted.

Here is a trick to improve this state of affairs that will benefit vegans, vegetarians and even meat eaters:

Simply add avocado to your carotene containing foods.

Compared to a raw carrot meal without avocado, the addition of one avocado (150 g):

• Significantly increases β-carotene absorption 6.6 times

• More than quadruples (4.8 times) α-carotene absorption

• Significantly increases (12.6 times) the conversion of provitamin A (inactive vitamin form) to vitamin A (active vitamin form)

It seems likely that avocado would also increase the absorption and conversion of carotenoids from green leafy vegetables or any other source. There is inherent wisdom in the way we have been preparing our salads - the fats from avocado and other oils we tend to dress salads with help with the absorption of the fat-soluble vitamin K1 found in green leafy vegetables as well as fat-soluble carotenoids like beta-carotene. The acid lemon or vinegar we add to salads may help with the absorption of minerals from leafy greens.

Eggs also improve absorption of carotenoids by as much as ninefold (as well as being a source of vitamin A) so for meat-eaters and vegetarians add eggs to your green leafy salads, or to meals including orange-fleshed squashes or carrots. Take care not to overcook the egg since this will oxidise the cholesterol which makes it damaging to your tissues. Soft or hard-boiled or poached eggs work well, whereas scrambled eggs will have the most oxidised cholesterol.

Even if you regularly eat liver and butter for vitamin A these tricks increase the absorption of carotenoids, which have their own protective antioxidant benefits aside from vitamin A formation. They have a powerful effect in turning genes on and off in a beneficial way, are associated with improved cognitive function and a decreased risk of developing obesity and a wide range of conditions including certain cancers (such as breast cancer), cardiovascular disease, Alzheimer's disease, type 2 diabetes mellitus and osteoporosis.

You are not likely to find beta-carotene as a supplement since it can actually be harmful when taken in isolation as demonstrated in a study of smokers whose lung cancer risk increased with beta-carotene supplementation. It is best enjoyed in the balanced range of carotenoids (such as α-carotene, β-carotene, γ-carotene, β-cryptoxanthin, zeaxanthin and lutein) you can find in:

• Green leafy vegetables
• Orange and yellow-coloured fruit and vegetables such as carrots, squash, melon (honeydew, cantaloupe, charantais), bell peppers, tangerines, oranges, sweet potato, mango, apricots, peaches and nectarines
• Papaya
• Egg yolk (high in lutein)
• Courgette (zucchini) and kiwi fruit (for lutein and zeaxanthin)