Puzzle Question: Does milk lactose increase heavy metal absorption?

It is a known fact that in babies, the lactose in milk aids in the absorption of minerals such as calcium from the intestinal tract. But, this process also increases the absorption of other minerals, even the heavy metal toxin Lead. An adequate amount of calcium in the meal limits the amount of lead that is absorbed. There is a calcium-lead interaction where one hinders the other if it is dominate.

This question came up due to studies on rats with lactose on lead. ref ref

This gives rise to the question: How does milk lactose influence the absorption of lead in adults? (Infants and children appear to mostly be protected by milk inhibiting lead absorption when consumed at same time)

Milk appears to be protective against lead absorption due to its calcium content. This reference gives some insights. ref

Increasing Vitamin D intake is associated with higher lead levels in blood, at least in summer. But in the absense of lead in the diet, vitamin D is protective and hinders lead coming out of bone. This may be part of the milk influence story. Vitamin D may influence lead by either increasing absorption from diet or by later hindering lead increase from bone into blood by vitmain D actions on controlling phosphate levels. When calcium to phosphate levels are good, lead in hindered from entering bone.

Vitamin C also presents a small dilemma. If consumed with lead, it increases lead absorption due to its binding ability with lead. But once vitamin C is in the body, This binding, or chelating ability, helps eliminate lead and vitamin C detoxicty antioxidant actions protect against some of lead induced damages. ref 

Adequate amounts in the diet of calcium, iron, and zinc help prevent lead absorption, probably by using up transport receptors that lead needs. ref

Obviously, it is best to limit lead exposure in foods and environment when known. Drinking waters are a potential source. Filters help. Plus some foods from their method of production are more likely to be contaminated, such as cereal grasses, wheat grass, rice, concentrated protein powders, and some sources of calcium supplements. Watch out for lead in pottery and leaded crystal containers, too.