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VITAMIN A IN VEGETABLES
477
THE LANCET LONDON: SATURDAY, APRIL 18, 1942
VITAMIN A IN VEGETABLES IN 1937 the adult’s requirement for vitamin A was assessed by a technical commission of the League of Nations at about 3000 IU a day. It was suggested that this intake could be assured by taking a pint of milk, one egg, an ounce of butter and a helping of green vegetable every day. Although no attempt was made at the time to differentiate between requirevitamin A, which is purely an for the vegetable pro-vitamin, these foodstuffs would contribute about carotene, 2000 IU of vitamin A together with 1000 IU of carotene. The war has greatly reduced supplies of dairy products, which are now available in generous amounts only for children and expectant mothers. The unprivileged adult receives no more than about 500-800 IU of preformed vitamin A daily. This includes the contribution made by margarine, which is vitaminised to a potency equal to about half that of good butter. Since commercial supplies of vitamin-A concentrates are probably too low to raise much hope of increased fortification of the margarine, and since we cannot all become cod-liver oil drinkers, the deficit in the intake must be made good by a greater consumption of vegetables. At first sight all that seems necessary is to raise the daily intake of carotene from 1000 to 2500 IU. But in fact we need ments for
animal
preformed product, and
to several outstanding problems before estimate accurately the amount of extra carotene which will be required. Thus the biological experiments which have enabled us to express quantities of preformed vitamin A in terms of the international unit, which is based on. carotene, have all been done with rats. There is evidence that in farm animals carotene is absorbed less completely than in the rat, and possibly the same may apply to man. In others words the unit of vitamin A, which for the rat has been fixed to be’exactly equal to the unit of carotene, may for other animals be worth considerably more than a unit. It is of crucial importance, therefore, to decide whether the official estimate of 3000 IU for the daily human requirement should refer to vitamin A or to carotene. Moreover, most experiments on the relative activities of vitamin A and carotene have been made with oily solutiona of the two substances. Can carotene be equally well absorbed from vegetable tissues, and if not how will the efficiency of absorption vary with different vegetables ? How will cooking, mastication and the individual powers of digestion affect the issue ? Attempts to answer some of these questions have already been made by many workers, who have approached them from different angles. It seems plain that in the human subject carotene is less well absorbed from the intestinal tract than vitamin A, since the faeces contain no vitamin A, but usually large amounts of carotene. Experiments in which the efficiency of absorption of carotene has been placed as low as 1 % may however be criticised on the ground of faulty methods of estimation. The available evidence suggests that the average efficiency may an
we
answer can
reasonably be taken as between 30% and 50%. Possibly a further loss may occur, reducing the total efficiency to about 25% in the case of man, when the pigment is converted to vitamin A after absorption
from the intestinal tract. It follows that if the official estimate of the requirement as 3000 IU was intended to refer to preformed vitamin A, it must be multiplied two to four times to be equivalently expressed in international units of carotene. If on the other hand it was intended to express the requirement in terms of carotene, the figure 3000 IU should be divided by between two and four when it is desired to express the requirement wholly in terms of preformed vitamin A. Whatever the ultimate solution of this’intricate problem, it does not affect the fact that during the remainder of the war we must rely on vegetables to supply the bulk of the national requirement of vitamin A. Under these circumstances the evaluation of the requirement in terms of preformed vitamin A becomes much less important than its assessment in terms of carotene, and particularly in terms of carotene as usually eaten in cooked vegetables. Such information seems particularly desirable in regard to the carrot, which must be reckoned as our main source of carotene on a large scale. Its gross carotene content, as estimated by chemical tests, is usually about 20,000 IU per 100 g., which means that even with very inefficient absorption the carrot must be a valuable of vitamin-A activity. Other--vegetables, source including spinach and broccoli tops, may be almost as rich, but they are available in smaller quantities over a shorter season, crop less heavily and cannot be stored. By the successful planning of the Ministries of Food and Agriculture adequate supplies of carrots were produced last year, and with an equal crop this season about 2 lb. per week per head of the population should be available throughout the year. Even though we do not know the exact requirement, efforts should be made to encourage everyone to consume this weekly share of half a pound as a safeguard to their health. The need for this must be frankly explained to the public. It is not enough merely to say " Eat more carrots," for this slogan will arouse no response in the indifferent and in those who do not like carrots ; the public must realise that since they can no longer get their pint of milk, egg and ounce of butter they must make up with carrots, helped out with vitaminised margarine. The campaign to introduce new and attractive ways of cooking carrots is a valuable step in this direction. There seems little point, however, in making particular efforts to boost the raw carrot. The carotene is not destroyed by cooking, and only’ small amounts of the heat-labile vitamins Bl and C are present in the roots even when raw. There is evidence, too, that cooking increases digestibility, with a corresponding increase in the efficiency of absorption of the carotene.
COMMISSION AND OMISSION EVEN before the outbreak of the present war the Medical Women’s Federation had -been in fruitless correspondence with the War Office regarding the status of medical women who might be invited to serve with the land forces. They were then told that in the event of another war no women doctors would be wanted in any capacity by the Army. But when the war came women doctors were asked to volunteer
THE LANCET LONDON: SATURDAY, APRIL 18, 1942
VITAMIN A IN VEGETABLES IN 1937 the adult’s requirement for vitamin A was assessed by a technical commission of the League of Nations at about 3000 IU a day. It was suggested that this intake could be assured by taking a pint of milk, one egg, an ounce of butter and a helping of green vegetable every day. Although no attempt was made at the time to differentiate between requirevitamin A, which is purely an for the vegetable pro-vitamin, these foodstuffs would contribute about carotene, 2000 IU of vitamin A together with 1000 IU of carotene. The war has greatly reduced supplies of dairy products, which are now available in generous amounts only for children and expectant mothers. The unprivileged adult receives no more than about 500-800 IU of preformed vitamin A daily. This includes the contribution made by margarine, which is vitaminised to a potency equal to about half that of good butter. Since commercial supplies of vitamin-A concentrates are probably too low to raise much hope of increased fortification of the margarine, and since we cannot all become cod-liver oil drinkers, the deficit in the intake must be made good by a greater consumption of vegetables. At first sight all that seems necessary is to raise the daily intake of carotene from 1000 to 2500 IU. But in fact we need ments for
animal
preformed product, and
to several outstanding problems before estimate accurately the amount of extra carotene which will be required. Thus the biological experiments which have enabled us to express quantities of preformed vitamin A in terms of the international unit, which is based on. carotene, have all been done with rats. There is evidence that in farm animals carotene is absorbed less completely than in the rat, and possibly the same may apply to man. In others words the unit of vitamin A, which for the rat has been fixed to be’exactly equal to the unit of carotene, may for other animals be worth considerably more than a unit. It is of crucial importance, therefore, to decide whether the official estimate of 3000 IU for the daily human requirement should refer to vitamin A or to carotene. Moreover, most experiments on the relative activities of vitamin A and carotene have been made with oily solutiona of the two substances. Can carotene be equally well absorbed from vegetable tissues, and if not how will the efficiency of absorption vary with different vegetables ? How will cooking, mastication and the individual powers of digestion affect the issue ? Attempts to answer some of these questions have already been made by many workers, who have approached them from different angles. It seems plain that in the human subject carotene is less well absorbed from the intestinal tract than vitamin A, since the faeces contain no vitamin A, but usually large amounts of carotene. Experiments in which the efficiency of absorption of carotene has been placed as low as 1 % may however be criticised on the ground of faulty methods of estimation. The available evidence suggests that the average efficiency may an
we
answer can
reasonably be taken as between 30% and 50%. Possibly a further loss may occur, reducing the total efficiency to about 25% in the case of man, when the pigment is converted to vitamin A after absorption
from the intestinal tract. It follows that if the official estimate of the requirement as 3000 IU was intended to refer to preformed vitamin A, it must be multiplied two to four times to be equivalently expressed in international units of carotene. If on the other hand it was intended to express the requirement in terms of carotene, the figure 3000 IU should be divided by between two and four when it is desired to express the requirement wholly in terms of preformed vitamin A. Whatever the ultimate solution of this’intricate problem, it does not affect the fact that during the remainder of the war we must rely on vegetables to supply the bulk of the national requirement of vitamin A. Under these circumstances the evaluation of the requirement in terms of preformed vitamin A becomes much less important than its assessment in terms of carotene, and particularly in terms of carotene as usually eaten in cooked vegetables. Such information seems particularly desirable in regard to the carrot, which must be reckoned as our main source of carotene on a large scale. Its gross carotene content, as estimated by chemical tests, is usually about 20,000 IU per 100 g., which means that even with very inefficient absorption the carrot must be a valuable of vitamin-A activity. Other--vegetables, source including spinach and broccoli tops, may be almost as rich, but they are available in smaller quantities over a shorter season, crop less heavily and cannot be stored. By the successful planning of the Ministries of Food and Agriculture adequate supplies of carrots were produced last year, and with an equal crop this season about 2 lb. per week per head of the population should be available throughout the year. Even though we do not know the exact requirement, efforts should be made to encourage everyone to consume this weekly share of half a pound as a safeguard to their health. The need for this must be frankly explained to the public. It is not enough merely to say " Eat more carrots," for this slogan will arouse no response in the indifferent and in those who do not like carrots ; the public must realise that since they can no longer get their pint of milk, egg and ounce of butter they must make up with carrots, helped out with vitaminised margarine. The campaign to introduce new and attractive ways of cooking carrots is a valuable step in this direction. There seems little point, however, in making particular efforts to boost the raw carrot. The carotene is not destroyed by cooking, and only’ small amounts of the heat-labile vitamins Bl and C are present in the roots even when raw. There is evidence, too, that cooking increases digestibility, with a corresponding increase in the efficiency of absorption of the carotene.
COMMISSION AND OMISSION EVEN before the outbreak of the present war the Medical Women’s Federation had -been in fruitless correspondence with the War Office regarding the status of medical women who might be invited to serve with the land forces. They were then told that in the event of another war no women doctors would be wanted in any capacity by the Army. But when the war came women doctors were asked to volunteer