IGF1 in Milk and Body Fluids39

Medium

Concentration (ng/ml)

Human milk

Human colostrum

Bovine (bulk milk, untreated)

Bovine (bulk milk, bST-treated)

Plasma (child)

Plasma (adolescent)

Plasma (adult)

Gastrointestinal secretions (saliva) Gastrointestinal secretions (gastric juice) Gastrointestinal secretions (pancreatic juice) Gastrointestinal secretions (bile) Gastrointestinal secretions (jejunal chime) Daily production of adult humans

17-250

180-780

120-460

It is also produced in the human gastrointestinal mucosa and is found in saliva, bile, and pancreatic secretions.127 Using the average IGF-1 concentrations of the five human gastrointestinal secretions,128 a molecular weight of 7.5 kDa for IGF-1,119 and the volume of each of the fluids produced,39 129 the total calculated mass of IGF-1 emptying into the gastrointestinal tract from these secretions is 383,000 ng/day (Table 7.6).

Blood IGF-1 concentrations are lowest in infants under two years of age, then increase steadily to reach a maximum late in puberty, and afterward decrease to adult values (Table 7.5). Assuming a blood volume of 5% of body weight, JECFA experts calculated the total amount of IGF-1 in serum to be 50,000 ng in a 15-kg child, 714,000 ng in a 60-kg adult, and 1,220,000 ng in a 50-kg teenager. The total daily IGF-1 production in adult humans has been estimated at 107 ng/day.131

Following review of the available data, JECFA39 concluded that ".. .any increase in the concentration of IGF-1 in milk from recombinant bST (rbST)-treated cows is orders of magnitude lower than the physiological amounts produced in the gastrointestinal tract and in other parts of the body. Thus the concentration of IGF-1 would not increase either locally in the gut or systemically, and the potential for IGF-1 to promote tumor growth would not increase when milk from rbST-treated cows was consumed; there is thus no appreciable risk for consumers." The JECFA dietary risk assessment is as follows: Assumptions:

• Average milk IGF-1 level from bST-supplemented cows is 6 ng/ml, from unsupplemented cows is 4 ng/ml.

• All the IGF-1 in milk can be absorbed intact from the gut (worst-case assumption — there is no evidence this occurs).

table 7.6

Concentration of IGF-1 in Digestive Fluids

Concentration of IGF-1 in Gastrointestinal Tract Secretions130

table 7.6

Concentration of IGF-1 in Digestive Fluids

Concentration of IGF-1 in Gastrointestinal Tract Secretions130

concentration

Total IGF-1

Secretion

Volume(ml/day)39

(Average; ng/ml)

Secreted(ng)

Jejunal chyme

1500

184.5

276,750

Pancreatic juice

1500

27.0

40,500

Gastric juice

2000

26.2

52,400

Bile

500

6.8

3,400

Saliva

1500

6.8

10,200

Total IGF-1 produced in one day in the gastrointestinal tract: 383,250 ng.

Concentrations of IGF-1 in Human Plasma129

Total IGF-1 produced in one day in the gastrointestinal tract: 383,250 ng.

Concentrations of IGF-1 in Human Plasma129

Males (ng/ml)

Females (ng/ml)

Age

Mean

Range

Mean

Range

0-2 years

42

14-98

56

14-238

3-5 years

56

59-210

84

21-322

6-10 years

98

28-308

182

56-364

Before puberty > 10 years

126

84-182

182

70-280

Early puberty

210

140-240

224

84-392

Late puberty

364

224-462

434

224-686

Adult > 23 years

112

42-266

140

56-308

The total intake of IGF-1 from consuming milk (1.5 L) from unsupplemented cows is 6000 ng versus 9000 ng for milk from bST-supplemented cows. The net difference for intake of IGF-1 is 3000 ng. The incremental daily ingestion of 3000 ng IGF-1 represents (3000/383,000) = 0.8% of the daily gastrointestinal secretion (383,000 ng/day). Considering that the total daily blood IGF-1 production in adult humans is estimated at 107 ng/day,131 the incremental amount of IGF-1 in milk is insignificant compared to the production of IGF-1 in adults, less than (3000/107) >0.03%. Even if all the milkborne IGF-1 were absorbed, the additional amount would be negligible.39 Another dietary risk assessment for IGF-1 in milk using U.S. consumption data for milk is summarized in Appendix 2; the conclusions were the same as those provided in the aforementioned JECFA dietary risk assessment.

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