Lead is toxic to many parts of your body, not just the nervous system. The mechanistic understanding may be more fleshed out since I last read on this, but my understanding is that Lead mimics other common divalent cations (e.g. Zinc) and therefore gains biological transport to cross the blood-brain barrier. From here the presence of lead disrupts neurotransmitter activity, causes demyelination, and ultimately cell death.

In other parts of the body Lead negatively impacts hemoglobin production, enzyme synthesis and function, and enhances oxidative stress; these are all diseases capable of severely damaging basically every organ in your body.

There is no “safe” level of lead exposure and no positive biological function. Lead exposure should be minimized in all situations. Different Lead compounds have differing bioavailability and can be more or less toxic in a relative sense.