46 The nutrition handbook for food processors 3.7.2 Safety of B-carotene Experimental studies with animals have shown that p-carotene is not mutagenic or teratogenic. In addition, doses of 180 mg/day have been used over many years to treat patients with erythropoietic protoporphyria, with no evidence of vitamin A toxicity(Blomhoff, 2001). B-Carotene is considered not to be toxic because bsorption becomes inefficient at high intakes, possibly because conversion of p- carotene and other provitamin A carotenoids is regulated by the vitamin A status of the individual. In two studies in which very different large intakes of B-carotene were given(15 and 40 mg), the mean absorption of B-carotene was <2mg sug- gesting the human intestine possess only a limited capacity to absorb B-carote (van Vliet et al, 1995; O'Neill and Thurnham, 1998) 3. 8 Vitamin Recognition of the antirichitic effect of meat fat in the 1920s, as well as the pre tective effects of sunlight led to the discovery of vitamin D. Vitamin D is the name given to a group of fat-soluble compounds essential for maintaining the mineral balance of the body. Vitamin d is also known as calciferol and the anti- rachitic vitamin and its principal function is to regulate calcium and phosphate metabolism. It has two main forms: ergocalciferol, vitamin D2(plant origin)and cholecalciferol, vitamin D,(animal origin) Vitamin D is produced from endogenous sources, synthesised in the skin from 7-dehydrocholesterol (7DHC)in a reaction catalysed by the ultra-violet (UV) light, and exogenous sources from the diet. There are only a few natural food sources, egg yolk, oily fish, butter and milk (Table 3.2). Margarines and spreads are fortified with vitamin d. vitamin d. either natural or added. is stable in foods cooking do not affect its activity. The normal human diet is, however, a trivial source of vitamin D, since the biggest source results from exposure to sunlight. However, vitamin D production by the skin is strongly related to latitude and season, because short UV wavelengths of light are neces- sary for photoconversion. This means that in the UK and other countries in the northern latitudes, sunlight during the winter months is ineffective for the pro- duction of vitamin d because the sun is so low in the sky, the absorption by ozone too great and Uv-B radiation too scattered(Maxwell, 2001). There are at least 37 metabolites of vitamin D(Norman, 1990) but only three 25 hydroxyvitamin D(25-OHD), 1, 25 dihydroxvitamin D3(1, 25-OHD) and 24, 25 dihydroxyvitamin D(24, 25-OHD) have any important biological activity Plasma 25-OHD is an index of availability of vitamin D and the normal range is 20-150nmol/L(8-60ng/ml). Values below 25 nmol/L (10ng/ml) indicate risk of deficiency and toxicity occurs at levels above 150nmol/L(60ng/mI). The average intake within the UK ranges from 0.5 to &ug/day, dependent on season, with a mean around 3ug/day. Table 3. 1 shows no DRV for those aged between 4 and 65 years as usual daily activity of able-bodied persons should provide sufficient exposure to UV light. The elderly and those confined indoors are recommended3.7.2 Safety of b-carotene Experimental studies with animals have shown that b-carotene is not mutagenic or teratogenic. In addition, doses of 180 mg/day have been used over many years to treat patients with erythropoietic protoporphyria, with no evidence of vitamin A toxicity (Blomhoff, 2001). b-Carotene is considered not to be toxic because absorption becomes inefficient at high intakes, possibly because conversion of b￾carotene and other provitamin A carotenoids is regulated by the vitamin A status of the individual. In two studies in which very different large intakes of b-carotene were given (15 and 40 mg), the mean absorption of b-carotene was <2 mg sug￾gesting the human intestine possess only a limited capacity to absorb b-carotene (van Vliet et al, 1995; O’Neill and Thurnham, 1998). 3.8 Vitamin D Recognition of the antirichitic effect of meat fat in the 1920s, as well as the pro￾tective effects of sunlight led to the discovery of vitamin D. Vitamin D is the name given to a group of fat-soluble compounds essential for maintaining the mineral balance of the body. Vitamin D is also known as calciferol and the anti￾rachitic vitamin and its principal function is to regulate calcium and phosphate metabolism. It has two main forms: ergocalciferol, vitamin D2 (plant origin) and cholecalciferol, vitamin D3 (animal origin). Vitamin D is produced from endogenous sources, synthesised in the skin from 7-dehydrocholesterol (7DHC) in a reaction catalysed by the ultra-violet (UV) light, and exogenous sources from the diet. There are only a few natural food sources, egg yolk, oily fish, butter and milk (Table 3.2). Margarines and spreads are fortified with vitamin D. Vitamin D, either natural or added, is stable in foods, and storage, processing and cooking do not affect its activity. The normal human diet is, however, a trivial source of vitamin D, since the biggest source results from exposure to sunlight. However, vitamin D production by the skin is strongly related to latitude and season, because short UV wavelengths of light are neces￾sary for photoconversion. This means that in the UK and other countries in the northern latitudes, sunlight during the winter months is ineffective for the pro￾duction of vitamin D because the sun is so low in the sky, the absorption by ozone too great and UV-B radiation too scattered (Maxwell, 2001). There are at least 37 metabolites of vitamin D (Norman, 1990) but only three: 25 hydroxyvitamin D (25-OHD), 1,25 dihydroxvitamin D3 (1,25-OHD) and 24, 25 dihydroxyvitamin D (24,25-OHD) have any important biological activity. Plasma 25-OHD is an index of availability of vitamin D and the normal range is 20–150 nmol/L (8–60 ng/ml). Values below 25 nmol/L (10 ng/ml) indicate risk of deficiency and toxicity occurs at levels above 150 nmol/L (60 ng/ml). The average intake within the UK ranges from 0.5 to 8mg/day, dependent on season, with a mean around 3mg/day. Table 3.1 shows no DRV for those aged between 4 and 65 years as usual daily activity of able-bodied persons should provide sufficient exposure to UV light. The elderly and those confined indoors are recommended 46 The nutrition handbook for food processors